Nanotechnology: Technical Basics and Applications 9783748602347

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Stefan Sepeur Nora Laryea Stefan Goedicke Frank Groß

Nanotechnology Technical Basics and Applications

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Cover picture: NANO-X GmbH, Saarbrücken, Germany

Bibliographische Information der Deutschen Bibliothek Die Deutsche Bibliothek verzeichnet diese Publikation in der Deutschen Nationalbibliographie; detaillierte bibliographische Daten sind im Internet über http://dnb.ddb.de abrufbar.

Stefan Sepeur Nanotechnology: Technical Basics and Applications Hannover: Vincentz Network, 2008 (European Coatings Tech Files) ISBN 978-3-7486-0234-7 © 2008 Vincentz Network GmbH & Co. KG, Hannover Vincentz Network, P.O. Box 6247, 30062 Hannover, Germany This work is copyrighted, including the individual contributions and figures. Any usage outside the strict limits of copyright law without the consent of the publisher is prohibited and punishable by law. This especially pertains to reproduction, translation, microfilming and the storage and processing in electronic systems. The information on formulations is based on testing performed to the best of our knowledge. Please ask for our book catalogue Vincentz Network, Plathnerstr. 4c, 30175 Hannover, Germany Tel. +49 511 9910-033, Fax +49 511 9910-029 E-mail: [email protected], www.european-coatings.com Layout: Maxbauer & Maxbauer, Hannover, Germany ISBN 978-3-7486-0234-7

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European Coatings Tech Files

Stefan Sepeur Nora Laryea Stefan Goedicke Frank Groß

Nanotechnology Technical Basics and Applications

Stefan Sepeur: Nanotechnology © Copyright 2008 by Vincentz Network, Hannover, Germany

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Foreword



Foreword You are holding our book about chemical nanotechnology in your hands. “Nanotechnology” – a concept that stirs a variety of emotions. In our professional environment, we have daily contact to people who are searching for solutions with the help of nanotechnology. Many have had previous experiences with the so-called “nanolayers”, others are familiar with terms such as “lotus” effect or “easy to clean” coatings. In the current literature, usually only a portion of the opportunities available through modern nanotechnology are described. This book is intended to provide an overview of all the important fields of chemical nanotechnology. We do not aspire to supply the reader with detailed information in all areas, but instead, we want to provide a structured overview of all the facets of this modern technology. The reader should be able to understand the diversity and opportunities of modern nanotechnology after reading this book.

The technical background for the most common applications of chemical nanotechnology is silane chemistry. With the help of silanes, the application possibilities can be divided into six steps. From the production of silica sols, to complex nanoparticulate filled materials in the form of multi-functional coatings – the interrelation is obvious in many areas.

The outline of this book is also arranged with regard to these reaction sequences. Starting with simple sol-gel reactions and the production of silica particles, we borrow aspects of glass chemistry, silicone chemistry and solid chemistry, to bring the reader closer, step by step, to the complex reactions of inorganic/organic nanocomposites. The subject matter of this book is based on comprehending and understanding the reaction mechanisms of modern polymer chemistry and the most important characterization methods. Where possible, all chapters list application examples, which are intended to demonstrate to the reader that these partially very simple, and partially very complex materials are already a part of our daily lives.

With this book, we hope to convey the fascination that chemical nanotechnology holds for us. The researchers that are working with these materials are finding new, previously unimaginable correlations and solutions daily. We wish you a pleasant journey on your way to discovering the nano-cosmos. Saarbrücken, Germany, April 2008

Stefan Sepeur, Nora Laryea, Stefan Goedicke, Frank Groß Stefan Sepeur: Nanotechnology © Copyright 2008 by Vincentz Network, Hannover, Germany

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Content



Content 1

Introduction to chemical nanotechnology.......................

11

2 2.1 2.2 2.3

Definition of nanotechnology............................................ General definition of nanotechnology................................. Definition of “chemical nanotechnology”........................... Nanotechnology for the field of “paints and lacquers”.......

13 14 14 14

3 Silane-technology as the key to chemical nanotechnology.................................................................. 3.1 Hydrolysis and condensation of silanes – principles of “sol-gel-process”............................................ 3.2 Network modifier for the flexibilization of the inorganic network................................................................ 3.3 Cocondensation of metal alkoxides in the Si-O-Si-network.................................................................. 3.4 Adjustment of surface effects.............................................. 3.4.1 Hydrophobic surfaces or the “easy to clean” effect............ 3.4.2 Super-hydrophobic surfaces or “lotus” effect..................... 3.4.3 Hydrophilic surfaces or anti-fog effect................................ 3.4.4 Superhydrophilic surfaces................................................... 3.5 Production and modification of nanoparticles..................... 3.5.1 Production of nanoparticles................................................. 3.5.1.1 Top-down: ball grinding...................................................... 3.5.1.2 Bottom -up: production from the gas phase........................ 3.5.1.3 Bottom-up: “Aerosil”-method............................................. 3.5.1.4 Bottom-up: chemical precipitation...................................... 3.5.1.5 Bottom-up: sol-gel-process................................................. 3.5.1.6 Bottom-up: microemulsion method..................................... 3.5.2 Surface modification of nanoparticles................................. 3.5.2.1 Stabilization of nanoparticles.............................................. 3.5.2.2 Special case of silanization.................................................. 3.5.3 Characterization of nanoparticles........................................ 3.5.3.1 Transmission electron microscopy (TEM).......................... 3.5.3.2 EDX-analysis....................................................................... 3.5.3.3 X-ray diffraction (XRD)......................................................

19 21 28 31 36 39 42 46 48 51 52 52 53 54 55 56 56 57 57 59 60 60 61 62

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Inhaltsverzeichnis

3.5.3.4 BET-surface classification................................................... 3.5.3.5 Photon correlation spectroscopy (PCS)............................... 3.5.3.6 Small angle X-ray scattering (SAXS)................................. 3.5.4 Utilization of nanoparticles for coating materials............... 3.5.4.1 SiO2-nanoparticles............................................................... 3.5.4.2 TiO2-nanoparticles............................................................... 3.5.4.3 TiO2-rutile for UV protection.............................................. 3.5.4.4 TiO2-anatase for photocatalytic effects................................ 3.5.4.5 Comparison between “catalytic clean” effect and “lotus” effect................................................................. Nanoparticles for diesel particulate filters........................... 3.5.4.6 3.5.4.7 Thermal degradation by nanoparticles................................ 3.5.4.8 CeO2- and ZrO2-nanoparticles............................................. 3.5.4.9 Carbon nanotubes................................................................ 3.5.5 Antibacterial effects............................................................. 3.5.5.1 Silver compounds for antibacterial coatings....................... 3.5.5.2 Chitosan for bacteria repellent coatings.............................. 3.6 Functional, organic network formers................................... 3.6.1 Reaction of a 3-glycidyloxypropyl trialoxysilane............... 3.6.1.1 Organic polymerization of 3-glycidoxypropyl trialkoxysilanes.................................................................... 3.6.1.2 Organic addition reaction of the 3-glycidoxypropyl trialkoxysilane..................................................................... Condensation of nanoparticles............................................ 3.6.1.3 3.6.1.4 Hydrolysis of 3-glycidoxypropyl trialkoxysilanes.............. 3.6.1.5 Variation of water amount................................................... 3.6.1.6 Variation of hydrolysis time-period..................................... 29 3.6.1.7 Si-NMR-spectroscopic examinations................................ 3.6.2 Reaction of 3-methacryloxypropyl trimethoxysilan (MPTS) 3.6.2.1 Inorganic modification with boehmite-nanoparticles.......... 3.6.2.2 Examination of viscosity..................................................... 3.6.2.3 Examination of temperature profile..................................... 3.6.2.4 Examining pH-level............................................................. 3.6.2.5 Model of particle stabilization............................................. 3.6.2.6 Characterization through transmission electron microscopy (TEM).............................................................. 3.6.2.7 Characterization by Karl-Fischer-Titration......................... 3.6.2.8 Characterization by 29Si-NMR-spectroscopy...................... 3.6.2.9 Characterization of organic crosslinking by FTIR- and photo-DSC measurements................................. 3.6.2.10 Influence of the boehmite concentration on the radical cross linking.........................................................................

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Inhaltsverzeichnis

3.6.2.11 Polymerization mechanisms and photo initiators................ 3.6.2.12 Flexibilization of the MPTS/boehmite by organic co-polymerization................................................................ 3.6.2.13 Examinations of the mechanical properties......................... 3.6.2.14 Classification of literature pertaining to nanocoatings based on MPTS.................................................................... 3.6.3 Precipitation emulsion method............................................ 3.6.4 Innovative bonding agent classification – “silixanes”......... 3.6.5 Corrosion protection............................................................ 3.6.5.1 Self assembling monolayers (SAM).................................... 3.6.5.2 Nanoparticle-filled siloxane coatings.................................. 3.6.5.3 Cathodic corrosion protectionwith nanoparticulate approaches........................................................................... 3.6.6 Protective coating against scaling for steel during hot stamping-nanotechnology combined with lacquer chemistry

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4

Outlook...............................................................................

153

5

Literature...........................................................................

155

List of abbreviations..........................................................

164

Authors...............................................................................

165

Index...................................................................................

166

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Introduction to chemical nanotechnology

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1 Introduction to chemical nanotechnology Nanotechnology is based on specifically manipulating the qualities and structures of materials on the nanoscale level. The term “nano” relates to the scale of the observed area: the nanometer (1 nm = 10 –9 m.) Nanotechnology (Greek nãnnos = dwarf) is a collective term for a wide selection of technologies, that are devoted to the research, design and production of items and structures that are smaller than 100 nanometers (nm.) A nanometer is a millionth of one meter (10 –9 m) and represents a limit range, in which the surface qualities, as compared to the volume qualities of materials, play an ever increasing role and the cumulative quantum physical effects must be given more consideration. Only a small branch of nanotechnology is focused on nanomachines or nanorobots. Even today, nanomaterials, which are most commonly produced chemically or with the help of mechanical methods, are of great importance. Due to his lecture entitled “There’s Plenty of Room at the Bottom,” held in 1959, Richard Feynman is considered the father of nanotechnology, even though the term “nanotechnology” was first used by Norio Taniguchi in 1974: “Nano-technology mainly consists of the processing of separation, consolidation, and deformation of materials by one atom or one molecule.” This implicates that the critical attributes of materials or devices can lie within the nanometer range, and that these materials and devices are constructed from individual atoms and/or molecules. The term nanotechnology is seldom used in this narrow sense today. In fact today, this term also implicates the production of nanomaterials by chemical means. In 1986, K. Eric Drexler made this term widely known, independently from Taniguchi. With his book “Engines of Creation”, he inspired many currently known scientists to study nanotechnology, including Richard E. Smalley (fullerene.) Drexler’s definition of nanotechnology is more precise than Taniguchi’s: it is limited to the construction of complex machines and materials out of individual atoms. According to this definition, current nanotechnology does not fall under Drexler’s perception of nanotechnology. This caused Drexler to differentiate his perception of nanotechnology in the 90’s, and rename it “Molecular Nanotechnology” (MNT,) because the term was and is often used to indicate all work involving nanostructures, even Stefan Sepeur: Nanotechnology © Copyright 2008 by Vincentz Network, Hannover, Germany

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Introduction to chemical nanotechnology

when normal chemical, pharmaceutical or physical methods were used. Drexler’s vision is contingent upon nanorobots, which influence or control our lives in the future. These futuristic theories are often used as models for modern science-fiction films. Nanotechnology is neither to be seen as an individual scientific discipline, nor as a defined field of application, but should instead be viewed on substantially broader terms as those indicated by Drexler. Therefore in 1998, Bachmann made sole reference to the order of magnitude for his general definition of nanotechnology. Accordingly, nanotechnology pertains only to systems, whose functionality and attributes are dependent solely upon the nanoscale effects of their components. This definition is certainly accurate for applications in the theoretical scientific field. But for the field of lacquer techniques, or in other words, for the daily development of materials, this definition is still too narrow. A lacquer technician, who achieves an improvement in the abrasion resistance by the integration of 2 wt.% nanoscale SiO2-particles in a coating system and can therefore compete in a new market, is just as much of a nanotechnologist as the microbiologist, who grows uniquely formed cells on chemical nanostructures. The relevant systems are influenced by nanoscale structures, but are not solely dependent upon them. One of the most unique aspects of nanotechnology is that is represents the multidisciplinary interaction of many specialized fields of expertise within the natural sciences. In this way, physics play an important role, simply for the construction of the microscope for examination purposes, particularly based on the laws of quantum mechanics. One uses chemical technologies to obtain a desired structure of matter and atomic arrangement. In the field of medicine, the selective application of nanoparticles should be helpful for certain diseases. But on the other hand, also biochemical structures, such as two-dimensional crystals, are constructed from DNA on a nanometer scale. Science has arrived at the point where the boundaries of the various disciplines become unclear, and one therefore refers to nanotechnology as convergent technology. In addition to the scientific theories, it means that in practice, the nanotechnologist focuses on functionalizing, miniaturizing, individualizing or examining materials and surfaces, to achieve new attributes. Nanomaterials play a prominent role in the field of lacquers and paints. The following chapters will give a reasonable definition of general nanotechnology for the lacquer and paint industry, define the special case of chemical nanotechnology, and essentially, present the possibilities and effects this technology offers the field of coatings in the context of application.

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Definition of nanotechnology

2

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Definition of nanotechnology

In general, the range between 1 nm and 100 nm is considered the range of nanotechnology. The concept of selectively allowing atoms and molecules to join together is referred to as “bottom-up strategy”. Creating nanoscale structures by the selective handling and milling of larger units is referred to as “top-down strategy”. For example in the field of microelectronics, this is achieved by using the lithograph procedure or special milling procedures. The developments leading to nanotechnology for the science of physics, biology and chemistry are displayed in Figure 2-1. By observing the example of electronics, or the computer industry, the development from “macro-” to “micro-” and on to “nanoelectronics” is easily recognizable. While the first mainframe computers of the computer industry filled halls or even buildings, through a continuing miniaturisation of the chip structures (top-down method,) it is possible to build high-performance computers that fit in a cabinet. Eventually, these

Figure 2-1: Top-down and bottom-up synthesis for the research fields of physics, biology and chemistry, within the scope of nanotechnology. Source: Verein der Ingenieure (VDI), Düsseldorf, (Engineers Association) www.vdi.de Stefan Sepeur: Nanotechnology © Copyright 2008 by Vincentz Network, Hannover, Germany

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Definition of nanotechnology

top-down methods reached their maximum potential. Therefore, new attempts for the production of chips target the bottom-up method, whereby these nanoelectronics are to be composed of atomic or molecular building blocks.

For the production of new substances in the field of chemistry, top-down method techniques are available in which microscale materials achieve a fragmentation into nanoparticles through grinding or ultra-sound techniques. The sol-gel technology is a classic method of bottom-up synthesis, with which the first SiO2-nanoparticles were already produced in the 1960’s, without being recognized as such, because the corresponding analysis was not yet available. A further bottom-up method of the chemistry sciences is the “Aerosil”-method, which will be further explained in Chapter 3.5.1.3.

2.1

General definition of nanotechnology

Nanotechnology is the systematic manipulation, production or alteration of structures, systems, materials, or components in the range of atomic or molecular dimensions with/into nanoscale dimensions between 1 nm and 100 nm (1 nm = 10 –9 m, or a billionth of a meter).

An attribute relationship is not directly included in this definition. For the definition of a technology, it is important that a systematic manipulation takes place and no coincidental or natural factors play a role. “Chemical nanotechnology” is a particular type of nanotechnology.

2.2

Definition of “chemical nanotechnology”

“Chemical nanotechnology” is the systematic production of systems, materials or components in the range of atomic or molecular dimensions with nanoscale measurements between 1 nm and 100 nm (1 nm = 10 –9 m) by means of chemical synthesis. This definition encompasses the entire field of paints and lacquers, so that every researcher who has dealt with nanoscale effects, can use this definition to describe his results.

2.3

Nanotechnology for the field of “paints and lacquers”

For approximately a decade now, the term “nanomaterials” has been receiving an increasing amount of interest. Since this time, particles of the size of under 100 nm, which used to be considered a phenomenon of colloid chemistry, have been subjected to new terminology and are now referred to as nanoparticles. The resulting intensive research of these nanomaterials has lead to new perspectives and many new interesting application possibilities: conventional chemistry of inorganic solids applies to compact matter, whose crystal phases and glass networks, including the structure of crystallite, and phase domains are being researched with the goal of

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Nanotechnology for the field of “paints and lacquers”

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developing methods for metal, ceramic and glass, with customized mechanical, thermal, optical, electrical or tribological attributes.

In the meantime, these results from the materials research are applied to nanoscale particles, that sooner resemble liquids or even gasses in their rheology. In modern physics, the so-called nanoparticles have long since established themselves as a further state of matter, along with gasses, liquids and solids. For the field of lacquer chemistry, nanoparticles or corresponding dispersions are used as an additive for coating materials, in order to keep up with the trend toward multi-functional surfaces. In connection with this, a special interest is given to the agglomerate-free integration of nanoparticles in coating materials. A certain component is generally perceived on the basis of its form and surface. Along with the pure coloring, surfaces now have a much broader spectrum of functions. Among the possibilities that are obtainable today are corrosion protection, scratchresistance, or “easy to clean”, etc. In the future, one will tap energy from house walls or use the street coverings to clean the air. In principle, many things are possible. But the development is just beginning to get started. The market and the development work in this area are in a state of constant growth. Under the right conditions, it is possible to integrate additional functions even into conventional paints.

Nanotechnology, or the miniaturisation of functionalities on the largest surface area possible, is a tool in these developments. Their proven and possible application ranges are extraordinarily versatile and encompass nearly all industrial branches from cosmetics, textiles, medical diagnostic, and on to the chemistry of materials and catalysts, as well as microelectronics, displays, optical cells and fuel cells, and up to themes relevant to the automobile industry such as scratch resistant paints and corrosion protection. Many of these modern applications of chemical nanotechnology are surface coatings, which have certain attributes via nanoscale phases. Along with the integration of particles, also the layer thickness can represent the relation to nanotechnology. Principally, one differentiates between four varying possibilities:

• One layer thickness in the range of 1 to 100 nm. This is used for certain surface modifications, such as for “easy to clean” effects.

• Coatings that form “in situ” nanoscale clusters during the manufacturing process, so-called nanostructuring, which cause special material attributes after hardening.

• Coatings, which are filled or functionalized through nanoscale particles. The coatings themselves can show significantly higher layer thickness (for e.g. the modification of clear lacquer in the automobile branch).

• Coatings, whose surface structures lie within the nanometer range (30 wt.% nanoparticles in the lacquer system, a detectible change of the attributes is ascertainable, which is usually not positive. Agglomerations and clouding occur, and also the biggest hurdle with high concentrations, a high level of brittleness. In the best case, only a moderate increase in the scratch-resistance is achieved.

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Definition of nanotechnology

Even if one determines, that the abrasion resistance is improved, often a decrease in abrasion resistance results due to the increasing embrittlement, such as with the micro hardness measurement. Practice shows: It is unfortunately not so easy to make these little reactive particles so compliant, that the addition of the nanoparticles into the lacquer systems actually leads to the desired effects. The silanes offer one possibility to combine inorganic solid chemistry, organic polymer chemistry and chemical nanotechnology together.

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Silane-technology as the key to chemical nanotechnology

3

19

Silane-technology as the key to chemical nanotechnology

One basic problem in using inorganic nanoparticles and their functions in organic lacquer systems, is their incompatibility with one another. Ionic bonds encounter covalent bonds, or salts encounter molecules and/or organic polymer structures. The occurring physical effects often can’t dominate the strongly aligned bond types, so that it inevitably results in the amalgamation and/or agglomeration of the inorganic particles. Furthermore, the particles, which are incorporated only as a bulking agent in the organic matrix, have a certain amount of mobility, which results in effects such as aging. The so-called silane offers one solution for this problem. The base atom of a silane is silicon (Si). Silicon is in the 4th main group, directly under carbon with the atomic number 14. Silicon is a classic metalloid and exhibits both the properties of metals as well as nonmetals. Pure, basic silicon possesses a gray-black color and exhibits a typical metallic, often bronze to bluish sheen. In its oxidized form, silicon appears as SiO2 and is renowned as the main component in sheet glass. As an element, silicon is unique, because along with the ionic bonds, it can also react in stable covalent bonds with carbon, even under normal conditions. These bonds, known as organosilanes, can be used as “bridge molecules” between organic and inorganic chemistry. Like demonstrated in Figure 3-1, on the one hand, the silicon can react by a splitting off of the OR groups, which are generally ethoxy- or methoxy leaving groups, as well as with other silanes, or even react with inorganic bonds or surfaces. The inorganic reaction of silanes to the network formation or to the creation of nanoscale structures or particles normally takes place as hydrolysis and condensation processes of silanes are referred to as the sol-gel-process [1].

Figure 3-1: Model of an organosilane silicon has the possibility to react with inorganic bonds and/or other silanes via the outlet groups labeled with OR, while simultaneously, a stable covalent bond to a hydrocarbon chain exists.

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Silane-technology as the key to chemical nanotechnology

The surface modifications of bulking agents of every dimension are referred to as silanization. These methods are also tools for the lacquer chemist to make the nanoscale dimension useable. The organic side of the model molecule shown in Figure 3-1 can be used for functionalizing as well as the polymerization into existing organic networks. The linkage possibilities that silane technology offers can be divided into seven reaction principles (Figure 3-2). As is evident in Figure 3-2, silane technology offers an unfathomable diversity of possibilities to model coating materials according to a given requirement profile. Numbers 1 to 6 each show the possibilities of how silane can react on the inorganic or organic side. Principally, all the various reaction possibilities go back to wellknown principles of chemistry.

Figure 3-2: Silane technology as an instrument for the chemical synthesis of nanostructured inorganic-organic units, or, for the direct synthesis of nanoparticles and/or as an instrument for the surface modification and stabilization of nanoparticles

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Hydrolysis and condensation of silanes – principles of “sol-gel-process”

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The modules are: • Glass chemistry, because one gets a silicate network during the linkage of silanes via inorganic condensation processes, which through co-condensation with metal oxides (for ex. Al, Zr, Ti...) create a change in the macroscopic properties (point 1 and 3 in Figure 3-2). • Silicone chemistry, because through short-chain organic side chains and the use of condensation catalysts, the formed chain length and/or the type and form of condensate can be adjusted very selectively. • Organic polymer chemistry, because the organic side chains of the silane can react with the known polymerizations from polymer chemistry or have addition reactions amongst themselves but also with other organic resins or molecules (No. 6 in Figure 3-2). • The ceramic material technology, because along with the production of nanoparticles, (No. 1 and 3 in Figure 3-2) through the possibility of surface modification, a random selection of ceramic particles and therefore additional solid-statespecific functions can be incorporated in the inorganic-organic matrixes (No. 5 in Figure 3-2). Every one of these special fields of chemistry and material sciences now fills whole libraries of literature. The creation of lacquer systems with special properties is especially interesting for the field of paints and lacquers, and that is the focus of this book. Through the continuous further development of silane technology and the sol-gelmethod, consistently easier ways are now being found for the production of surface coatings with multi-functional properties, which surpass the best available technology of organic coatings with completely new properties or property profiles. In some cases, new markets are being created by the utilization of these new materials, and in some cases, a predatory competition develops with conventional lacquers, as with the development in the field of clear lacquers for automobiles. In order to understand the entire range of possibilities of silane technology for chemical nanotechnology, in the following seven chapters, according to Figure 3-2, the individual reaction possibilities with their chemical basis and technical application will be clearly explained.

3.1

Hydrolysis and condensation of silanes – principles of “sol-gel-process”

Tetraethyl orthosilicate is a special case of a silane (Figure 3-3, page 22). Tetraethyl orthosilicate (TEOS) in its condensed form, forms a pure SiO2-network without organic modification. For this reason, TEOS is especially suitable for

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Silane-technology as the key to chemical nanotechnology

explaining the principles of hydrolysis and condensation via the sol-gel-process.

Figure 3-3: Simplest condensation unit from a hydrolyzed tetraethyl orthosilicate (TEOS)

The sol-gel-process in general, demonstrates a method of synthesis of inorganic network structures. For a better overview, in the first step, we will limit ourselves to a simplified form of illustration, of how the acid catalyzed hydrolysis and condensation of TEOS transpires.

As seen in Figure 3-4, the ethoxy groups are hydrolyzed under acid catalysis and become reactive OH-functions, which can, in a second step under dehydration, be condensed with one another and become a network. In reality, the reactions are far more complex then portrayed in Figure 3-4, as will be explained in more detail in the following. In the primary step, monomer silicic acid esters such as TEOS, but also other metal alkoxides, are transformed into reactive monomer hydroxyl compounds (Equation 1). Equation 1

Me(OR) n +m H 2O  →Me(OR) n −m (OH ) m +m ROH

Me = (Half-)Metal Si, Al, Ti, Zr, ... R = organic moiety

The thus obtained reactive monomers are now capable of linking together by means of a condensation reaction. This process can be described by using the Equations (2) and (3): Equation 2

≡ Me − OH + HO − Me ≡  →≡ Me − O − Me ≡+ H 2O

Equation 3

≡ Me − OR+ HO − Me ≡  →≡ Me − O − Me ≡+ROH

Me = Si, Al, Ti, Zr, ... R = organic moiety, for ex: Ethyl, Methyl, Propyl etc.

Figure 3-4: Model demonstration of hydrolysis and condensation of tetraethyl orthosilicate (TEOS)

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The reaction speeds of the condensation reaction in Equation (2) and Equation (3) are influenced by medium, concentration and temperatures and run parallel after the start of the hydrolysis [2]. According to Equation (1), through the different hydrolysis stages of the alkoxide, colloidal solute oligomers (sol-condition) can be produced in a variety of ways in the resulting condensation step, which can crosslink to three-dimensional polymer structures (gel-condition) [3]. By using appropriate methods, the sol-phase can be stabilized as a transition state to a three-dimensional network. For this, a control of the reaction conditions and the acknowledgement of corresponding factors of influence to the hydrolysis and condensation stages in the sol-gel-process are necessary. Experiments for the hydrolysis and condensation reaction of tetraethyl orthosilicate (TEOS) have shown, that the pH-value has a deciding influence on the hydrolysis and condensation speeds of alkoxide compounds [2]. It has been determined, that in the pH-range between pH 0 and 2 under the chosen conditions, the balance of the reactions hydrolysis-condensation tips to the side of hydrolysis, or in other words, structures are formed with a high hydrolysis level and a low condensation level. Under comparable conditions in the alkaline pH range, the scales tip toward the side of condensation, or in other words, after the slow formation of hydrolyzates, the condensation reaction begins immediately, whereby separate highly crosslinked polysiloxane units are formed, whose terminal group is affected by incomplete hydrolysis (high -Si(OR)x residue, Figure 3-5) [4–5]. For example, this plays a very big role in the production of nanoparticles from alkoxides, which generally takes place in the alkaline environment. Far reaching fundamental experiments have shown, that the structure of the formed condensate, apart from the pH-value of the reaction medium, are dependent upon the type of solvent, the type and chain length of the alkoxide function (methyl, ethyl etc.), the concentration, the temperature, the type and concentration of the catalyst, evaporation speed as well as the water amounts added [2, 6–12]. The first studies of the hydrolysis of tetraethyl orthosilicate (Si(OEt)4,

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Figure 3-5: Structure model of inorganic network structures in varying pH-ranges

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Silane-technology as the key to chemical nanotechnology

Figure 3-6: The conversion of tetra-alkoxysilane by using the sol-gel-process: through hydrolysis and condensation, a sol is formed, which is transformed to gel through aging and/or drying. Drying under increased temperatures (sintering,) results in the formation of SiO2-nanoparticles.

TEOS) were published already in the 19 th century, which lead to the SiO2-sols [13–15]. The first commercial SiO2-powders on the sol-gel basis were then developed in the 1950’s [16].

The method has now been so refined, that sols made of nanoscopic SiO2-particles in the size range of 5 to 50 nm are produced. During film casting or spin-coating on substrates, these sols transform themselves, initially by particle aggregation, into lyogels. Ceramic fibers can be spun from this state. However, in most cases, the lyogel is dried to xerogel1, which can then be sintered to ceramic [17–20]. Extremely hard ceramics can be produced because the nanoparticles from the gel state, which can be adjusted and controlled in a well-defined manner in all stages of the process, can be very compactly sintered (Figure 3-6). Strict observation must be given to the structure of the gels. The lyogel is composed of a matrix of a dispersing agent, which is traversed by a SiO2-percolation network. This lyogel complies exactly to the definition of a gel: Gels are easily deformable, but dimensionally stable disperse systems, which consist of a firm, loose, three-dimensional network, which traverses the matrix of the dispersing agent. In simplified terms, this means: a pre-condensed network (in our case siliceous), soaked with solvent and with the consistency of jello (which incidentally, is also a gel). Every chemist, who has studied sol-gel-chemistry, will eventually and unavoidably gain experience with gel formation.

Xerogels, or the product after the drying of the lyogel, based on the example of silicates, consist only of aggregated SiO2. In this case, the general gel-definition no longer applies, because the medium no longer exists, which gives the gel its jelloconsistency. During the drying process of lyogel to xerogel, the fractal, precrosslinked SiO2-Network remains locally, but the body shrinks as a whole. Finally in the curing phase, in which the condensation is completed, the xerogel is sintered to a compact, monolithic ceramic. 1 L  yogels are firm, gel-like phases with a three-dimensional network, which have pores that are filled with a liquid or a solvent. If the liquid is water, it is referred to as hydrogel. Should the liquid medium in the pores be exchanged for gas (air) during the drying process, then it is a xerogel. (see also Figure 3-7)

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Figure 3-7: The synthesis from a xerogel from the sol state, via the transition step of lyoand/or hydrogel.

In some cases, the network of the lyogel can survive the drying process intact. For drying under hyper-critical conditions, it is possible to remove the dispersing – and/ or solvent agent so carefully, that the naked network remains as a highly porous aerogel – a xerogel filled with air (with a very low density of 0.08 g/cm3) [20]. These can also be used as absorbers, filters or drying agents. With other variations of the sol-gel-method, apart from silicate, also titanate, zirconate- and aluminate-ceramics and surface coatings were produced. Sol-gel-synthesis is not only used for nanoparticles. Microparticles with a diameter of over 100 nm are produced in even more variety, not only as an oxide, but also various types of salt. Depending on precursor and the conditions, particles are formed with a relatively uniform size of spheres, but also in anisotropic forms such as needles, polygons or platelets [21]. It is evident from the recipes of the literature, that for the production of such particles, there are often neither chemical nor physical guidelines or models. SiO2 is to be seen as the one exception, by which the controlled production of extremely well-defined microparticles was successful. The sol-gel-synthesis of sols with mono disperse, micro- and nano-SiO2-particles with a spherical form were described already in 1968 by Stöber and is recorded in literature as the Stöber-process [22]. Initiated by Stöber’s research, the production and stabilization of silicate sols received vast practical significance already as of the 1970’s, because the sol intermediate-stage can be used, for example: • • •

as coating materials as a medium for the surface modification of nanoparticles or as the production reaction for nanoparticles.

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Silane-technology as the key to chemical nanotechnology

Figure 3-8: Sol-gel-method: Stöber-process for the production of monodisperse SiO2particles from a tetraethyl orthosilicate through ammoniacal hydrolysis and condensation

These particles were and are intended for utilization in dispersions and composites, where they should be dispersed in a particular form, which is why the all important gel-formation must be avoided in ceramic production. In the Stöber-process, liquid or solid aliphatic orthoester of silicic acid (orthosilicate, Si(OR)4), e.g. TEOS, which serves as a precursor with watery ammonia as a catalysis and stabilizer, are hydrolyzed and condensed in an alcoholic solution. Ammonia complexates the resulting particles, which slows down the particle growth process. As a result, the steps of nucleation and particle growth are separated from each other, which is why all the particles grow to approximately the same size at the same speed [23]. Uniformly spherical silica with varying diameters (0.2 to 1.2  m) can by synthesized in an alcoholic medium by the hydrolysis of tetraethyl orthosilicate (TEOS) in the presence of water and ammonium hydroxide. The size of the spherical silica particles is relative to the start-concentration of the water and ammonia, as well as the TEOS and alcohol. Particle sizes starting at one micrometer can be achieved by the successive addition of the individual reactants. Both the pH-value and the temperature are important parameters, which

Figure 3-9: SEM view of spherical silicium dioxide particles

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also have influence on the crosslinking and therefore also on the size of the particles produced. First, water, ammonia and alcohol are heated to 40 to 45 °C, and TEOS is added subsequently. For silica with a larger diameter, a two-step reaction is conducted. A starting-amount of TEOS is mixed with alcohol, water and ammonia. After 30 minutes reaction-time, under gentle stirring at 40 °C, the remaining amount of TEOS is added. Through experiments, it was determined, that the Stöber-process (model in Figure 3-8) can be influenced in the following ways [24]: • • • • •

Residue R: The hydrolysis slows down as the chain length of the leaving group increases, or from R = methyl to R = pentyl, by which the particle growth is stimulated.

Residue R: The SiO2-spheres grow from R = methyl to R= pentyl from diameters under 100 nm to over von 1 μm, or with the increasing chain length of the leaving groups, the particle size increases.

H2O-content: With a low water surplus, small particles are formed, with a high surplus, a maximum of sphere-size is processed.

NH3-content: More ammonia leads continuously to larger spheres, so that a maximum of saturation concentration is achieved. Temperature: Heating the SiO2-sols benefits the gel process. Extremely finely grained nano SiO2 is produced, if one works with very little ammonia and water.

The Stöber-process is carried by the reaction steps of hydrolysis and condensation. If hydrolysis occurs much more quickly than condensation ( hyd >> cond), both processes can be clearly separated from one another. The acid accumulates in high concentration and forms a high quantity of seed, that cannot, or can barely grow. In the opposite case, if the acid concentration stays low, only a small quantity of seed is formed, which then grow to large particles. In general, it can be determined, that the alkaline hydrolysis leads to compact, large particles (such as with Stöber-process), whereas the quicker acidic hydrolysis, which is however more difficult to control, leads to nanoparticles that tend to aggregate fractally. SiO2-sols have found a variety of applications in the meantime. Unmodified systems are used to polish, as fire-prevention materials (e.g. for wood) or as an additive to water-based lacquers. The sol-gel-chemistry, along with particle synthesis, offers a significantly larger application range through the integration of organic side chains. The spectrum reaches from inorganic-glass-like materials to inorganic/ organic composite materials.

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3.2

Silane-technology as the key to chemical nanotechnology

Network modifier for flexibilization of inorganic network

A distinctive property of silicon is its ability to connect covalently to organic side chains. One has the possibility to combine the principles of inorganic and organic chemistry in one molecule. Materials obtained by the sol-gel-process, in which covalent organic groups can be integrated into an inorganic network, are referred to as inorganic-organic composites [25]. These are obtained by hydrolysis and condensation reactions, for example, based on modified silicon alkoxides. One has the following model of a partial step in hydrolysis – (4) and condensation, based on the example of methyl trialkoxysilane [26]: Through the condensation process (5), one obtains a three-dimensional network with an organically modified inorganic framework, the properties of which can be determined, depending on the type of organic residue, by the process [27]. The controllable fiber dimensions of the inorganic-organic components normally lie in the molecular – to nanometer range (≤ 5 nm). Because the curing temperatures are lower than the decomposition temperatures of the organic materials, it is possible to synthesize multi-component materials. The drastic reduction of the agglomeration temperatures for organically modified networks in comparison to pure inorganic networks, is attributed to the enhancement of the relaxation possibilities through network modifiers.

Figure 3-10: Methyl trialkoxysilane as an example of a network modifier in sol-gel-chemistry

Inductive, or electronic influences on the reactiveness are substantiated by experiments on organo alkoxysilanes (RxSi(OR’)(4-x)). Schmidt et al have shown that the speed of hydrolysis of organically modified alkoxysilanes with short alkyl groups R on silicon, are significantly higher,

Equation 4: Hydrolysis

Equation 5: Condensation

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Figure 3-11: Hydrolysis of an organo silane through the SN1-and SN2-mechanism. Long organic side chains R with a strong inductive effect of electrons (+I-effect) tend to lead to an SN1-reaction with silicon cations intermediate stage

in the case of acid catalysis, than the corresponding tetra-alkoxysilane [28]. A SN1reaction by a silicon-cation (≡Si+) is adopted as a mechanism, which can be stabilized by inductive effects (+I-effects) through the covalently connected alkyl groups, and make it possible to add water quickly (Figure 3-11). Pohl and Osterholtz [29] as well as Mc Neil et al [30] have determined in their experiments relating to the reaction speed of alkoxide silanes, that they experience an accelerated abreaction in buffered aqueous systems compared to tetra-alkoxysilanes, both under acidic as well as under alkaline catalysis. Along with the steric effect of a non-hydrolysable side group R, a stabilizing of the hydrolyzed phase results also from the +I effect, which the carbon chain develops. As a result, the condensation speed, compared to tetraethyl orthosilicate, is significantly reduced [31]. The sol-gel-process is controlled by the organic side chain in such a manner, that a sol with a low condensation tendency is produced after an accelerated hydrolysis. This is used for the manufacture of low-sintering coating solutions. The simplest modification is methyltriethoxysilane (MTEOS), in which a siloxane group is replaced by a methyl group (Figure 3-10 above with R = Ethyl). If such a MTEOS-sol is applied to surfaces and cured in a convection oven, they are given a transparent, relatively abrasion-resistant film, that does not show crack formation even at a layer thickness of >5  m. In comparison, cured layers made of hydrolyzed TEOS showed hairline

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Figure 3-12: Examples for silanes with organic side chains (organosilanes), which can be used as network modifiers

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Silane-technology as the key to chemical nanotechnology

cracking already at a thickness of 0.5  m. Depending upon the chain length and the number of modifications to the silicon, varying flexibility levels can be adjusted. An exception is the use of dimethyl dimethoxy silane as a basic element of silicone chemistry (Figure 3-12). If one observes the possible condensates between methyl-, dimethyl- or phenyl silanes, one can determine, that polymers are produced that are useful to the lacquer chemist, namely silicone resins such as methyl silicone resin, phenyl- or methylphenyl silicone resin. These are noted for high chemical-, temperature and weather resistance and are used as an adhesive agent in many modern lacquer systems, or as a hydrophobicity agent (additive). Silicones, known as polyorgano siloxanes in chemistry, are similar in structure to organically modified glass. They are composed of a framework, that is normally only two-dimensionally interwoven and is alternately constructed out of silicon and oxygen. This framework can be modified in a variety of ways through organic, carbonaceous groups. The basic component of silicones is dimethyl siloxane, which is either gaseous, liquid or solid, depending on the condensed chain length. Nearly all silicon products are a derivative of three raw material groups: • Silicone oils • Silicone rubber • Silicone resin Silicone products have special attributes, such as a high resistance to heat and cold, a water repelling effect, electrical insulation attributes, high elasticity, good separation ability, and especially good environmental compatibility due to their simple chemical configuration. Many applications in the automobile industry can be problematic, due to the lowmolecular (short chained) components, which diffuse gaseously and lead to significant wetting problems (“crater formation”) on surfaces. However, this reaction is generally not observed in the largely three-dimensional sol-gel-systems, which gives them a huge advantage, especially in the automobile industry. Due to higher crosslink density, such “glass-like” systems often tend to form embrittlement cracks. Examples of applications for silicone resin are coatings in the construction industry, decoration- and industrial lacquers, packaging lacquer, ship- and protective lacquers, dispersion paints, etc. Also in the silicone industry, nanotechnology now receives a high importance level. The boundaries and fields of development between modern sol-gel- and commercial silicone chemistry are becoming increasingly nebulous, because both technologies are similarly constructed chemically, and the positive attributes of both technologies and production methods are easily combined.

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Cocondensation of metal alkoxides in the Si-O-Si-network

However, the modification possibilities of sol-gel-chemistry are not only restricted to flexibilization of inorganic matrices and having access to high temperature stable binders. In the following chapter, the possibilities of functionalizing the inorganic matrix through cocondensation of alternative inorganic compounds will be described.

3.3

Figure 3-13: Cocondensate from a metal alkoxide (Me= Al, Ti, Zr, Ce,..). and silicic acid

Cocondensation of metal alkoxides in the Si-O-Si-network

The possibilities of modifying the inorganic network are known from the field of glass chemistry. Through the application of the alternative metal alkoxides or soluble metal salts (CeCl3, NaF, …) in the sol-gel-process, along with the homocondensation under the formation of siloxane bonds (≡Si-O-Si≡), a cocondensation occurs under the formation of heteropolar bonds, which can influence the physical characteristics such as the refraction index, flexibility, UV or IR transparency, or also the chemical stability of the system [32]. Table 3-1 shows a short overview of the common fields of application for the modification with metal salts or metal alkoxides. Only a few of the most important metal bonds are listed in Table 3-1, which are used in practice. In principle, fantasy knows no bounds, or in other words, when Table 3-1: Overview over effects and application of metal alkoxides and soluble metal salts in the sol-gel process Alkoxide/salt

Effect

Application

Al(OR)3, Zr(OR)4

Lewis acid, catalyst for inorganic crosslinking, catalyst for organic crosslinking e.g. epoxy polymerization, improvement of chemical stability, particularly alkaline stability of the inorganic network

scratch resistant coatings, corrosion protection, adhesion promoter, additives for improvement of chemical stability and scratch resistance

Ti(OR)4

increase of refractive index, catalyst for inorganic crosslinking, photocatalytic activity

anti-reflective coatings, scratch resistant coatings with high refractive index (e.g. eyeglass lenses)

Li, Na, K, B-salts

network modifier, formation of SiO-Na+-“defects”

binder, glass-like coatings for metals as a protection against tarnishing or anti-fingerprint coatings

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using a TEOS-hydrolyzate and an ethanol-soluble salt or alkoxide, one can combine any arbitrary combination from a SiO2-network with respective “foreign ions” or contaminations. Naturally, if such a solution is available, one can also synthesize nanoparticles with varying compositions [33] through alkaline precipitation reactions (Stöber synthesis, see Chapter 3.1) according to the principles of the sol-gel-method. The metal ions can perform various functions, which pertain, on the one side to their charge, and on the other side, to the size, the electric negativity and the occupation of the outer electron shells. For instance, this is how sodium, lithium or potassium ions are used to make the network more flexible. Imperfections in the silicate network occur, because these ions can only have one charge (monovalent alkali ions). This rule applies: the bigger the ion, the bigger the imperfection and therewith also the expansion of the network. These imperfections have the positive effect of making the network more flexible, or in other words, the brittleness is reduced, and a higher layer-thickness can be achieved. Furthermore, the alkali resistance is generally increased, because through the modification with monovalent ions, the entire network is alkaline based. The disadvantage is, that the hydrolysis resistance, or the resistance to water and moisture is significantly reduced. This turns into water solubility, if there is a very high alkaline content. Such systems can be purchased commercially under the name of “water glasses”. An interesting possibility with these alkaline systems from modified Si-O-Si-structures is the ability to apply a layer-thickness of more than 3  m of pure glass. These systems find application as protective coatings for scratch-sensitive glasses (sapphire glass) or for high-temperature protection against tarnishing and scratch resistance for stainless steel, for ex. for iron-soles or also for the reduction of contamination of valve caps. In some cases, these systems are used as a replacement for enamel. The requirement for avoiding water solubility and for designing such materials for practical use is the reduction of the ion content in the system. This can take place in two different ways. For one thing, disodium oxalate can be added in small quantities, as an additive in the sol-gel-process during the hydrolysis of TEOS. In order to immediately adjust the alkaline medium, it is also possible to hydrolyze TEOS specifically, with sodium- or potassium hydroxide solution under a reduced water addition. A further synthesis option is found in the high-alkaline water glasses. These are aqueous and do not mix well with alcoholic TEOS hydrolyzates. However, in order to reduce the sodium content, one can easily mix with a silica sol (SiO2-nanopar-

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ticles in suspension) or disperse them in the “Aerosiles”, or the so-called pyrogenic nanoscale SiO2-particles. After the firing process, the ions, such as sodium ions, distribute themselves evenly in the system. One “dilutes” the number of ions in the SiO2-network. The firing process temperatures of such materials generally lie beyond 500 °C, which limits the substrate selection and therefore also the application ranges to steel, ceramic, and glass surfaces. In order to avoid stainless steel tarnishing, the firing must take place under a protective gas, which generates additional costs and makes this technology only of interest to the niche markets.

Aluminum- or zirconium alkoxides are used as inorganic hydrolysis- and condensation catalysts and therefore also for increasing the glass strength. Both bonds are Lewis acids. The effects of the condensation of aluminum oxide in the SiO2-network are known from ceramic stove tops. In this case, by using a Si-O-Al-mixture, a significant increase in scratch resistance and an improvement in the chemical durability of the glass and or the glass ceramic are achieved. Zircon glasses are used for the storage of chemicals. If one replaces the TEOS-hydrolyzates with aluminum alkoxides, a significant increase in chemical resistance is achieved [34–35]. Coatings of only very few nanometers layer-thickness already show a significant improvement of chemical and mechanical attributes at curing temperatures of only 80 °C, e.g. with shiny chrome surfaces. The disadvantage is, that the brittleness of a pure SiO2-layer compared to an Al-OSi- layer remains practically identical, and one can only produce a flawless coating layer thickness of a maximum of 300 to 400 nm. Such systems find application primarily on chrome surfaces or as a chemically resistant coating on glass. In connection with organically modified silanes, such as MTEOS, aluminum- and zircon alkoxides are often used as a curing- or condensation catalyst. In general, the reaction manipulation of sol-gel-systems under the inclusion of aluminum and zirconium alkoxides is a challenge for the scientist. Nanoparticles form automatically with a higher water content in the reaction medium, in a socalled “in situ”-synthesis. Under the conditions of a normal sol-gel-reaction, or in a slightly acidic medium under controlled water addition, the condensation tendency is the greatest for the formation of Al-O-Al-condensates. Then follows Zr-O-Zr-condensates and finally, with the least condensation tendency, Ti-O-Ti and Si-O-Si. That means concretely, for the condensation processes according to a parallel reaction of silicon alkoxides

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Figure 3-14: Reaction possibilities for silicon and aluminum alkoxide. Hydrolysis and homocondensation (above, below) as well as heterocondensation (middle)

and metal alkoxides, that in both the cases of Zr- and Al-condensation, amorphous nanocondensates are created, which are covered by the less active Si-condensates and linked together. The possible reaction channels are presented based on the example of silicon and aluminum alkoxide in Figure 3-14. After the hydrolysis of the corresponding lead compound, either a homocondensation can now run between two silanol groups (Si-OH) and/or between two aluminum hydroxide groups (Al-OH) or a heterocondensation between Si-OH and AlOH. The condensation of two Al-OH groups is kinetically the most favored in this case. As a result an amorphous Al2O3-nanocondensate will form in an amorphous SiO2-matrix (bottom equation in Figure 3-14). Of course, it is also possible to avoid the formation of these “in situ” nanoparticles. In order to do this, the joint hydrolysis and condensation reaction must take place in a strongly diluted solution and with the lowest possible addition of water. Depending upon reaction manipulation, one can detect partly drastic differences in the macroscopic attributes. In the case of Si-O-Al-networks the homogenous condensate can show a significantly higher resistance against alkali than the same composition under the formation of nanocondensates. The scratch and abrasion resistance is increased in the systems containing nanoparticles. If one hydrolyzes Ti- and Si-alkoxides under normal sol-gel-conditions, the condensates tend toward a more even distribution. This is useful for the production of anti-reflection coatings. Along with good dielectric qualities ( r ~100), titanium oxide (TiO2) also shows a high refraction index of approx. 2.5 (Anatase: 2.55;

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Rutile: 2.75). SiO2 had a refraction index of 1.46. Through thin repeated coatings and a mixture between TiO2 and SiO2, one can drastically reduce the optical reflexes. An additional way to avoid refraction between substrate and air, functions by building up a refraction value gradient, sometimes through a structurising of the surface (moth-eye structure) or through a specifically adjusted porosity in a SiO2-network, so that the transitions between the refraction value air/substrate will flow smoothly. The reduction of surface reflection on eyeglass Figure 3-15: Anti-reflection lenses, and also for modern display technology is coating on a glass pane [36] state-of-the-art today. The application of moth-eye structures for polymer surfaces with transparent coverings in automobiles already standard. For the chemist in the paint and lacquer industry, this optical effect is only obtainable through multiple coatings or structurising. Putting an additive into an existing clear-lacquer system is not possible due to physical laws. At this point, let’s just say that with regard to additional effects in common lacquer chemistry, which is made possible by modern nanotechnology and sol-gel-chemistry, a change of thinking is necessary. Up until now, it was customary for the lacquer chemist to simply stir in an additive that corresponded to the attribute he wanted to integrate into the system, and the functionality was produced. Such simple methods fail with physical effects such as anti-reflection coatings, anti-fingerprint on glass or also the “lotus” effect. As Sherlock Holmes would say: “When one eliminates the impossible, whatever remains – however improbable – must be the truth.” Law of logic would claim it makes sense to become acquainted with these new effects. The expectations of desired effects and the natural scientific reality can often be strongly divergent. The cocondensation of various precursors in the sol-gel-process can lead to the spontaneous formation of nanoparticles according to the “in situ”-method, but this does not definitely occur. The nanoparticles can take over a positive property function, but the opposite can also take place. The diversity of the reaction possibilities and the resulting material properties of a coating are actually quite vast. In the case of sol-gel-controlled particle manufacture or surface modification, it is important for the paint and lacquer chemist to pay close attention to the conditions, under which the reaction is controlled, which have an extreme influence on the end result and must be accordingly heeded.

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Not only the matrix can determine the properties of a coating, but also the interface and especially the surface offer a variety of possibilities. From hydrophobic to hydrophilic, certain macroscopic properties are connected to surface effects, which we will explain in Chapter 3.4.

3.4

Adjustment of surface effects

So far, we have examined the property profiles solely through changes to the composition of the matrixes. A further degree of freedom with silane coatings is the adjustment of specific surface energies, which is demonstrated in the general summary under number 3 in Figure 3-2. This can be achieved both directly on surfaces, and also by using the additive process for existing lacquer systems. Catch phrases that are used in connection with nanotechnology are “lotus” effector “easy to clean” surfaces, anti-fog effect or self-cleaning. In reality, the diversity of these effects is vast, but is only secondarily related to nanotechnology. In order to get a better understanding of the effects, and of which effects are best suited for which fields of application, the diverse possibilities and terms for various surface energies will be explained and discussed in this chapter. The relationships between surface energy, wetting, the resulting contact angle, and the macroscopic effects in the form of easy- or self-cleaning surfaces will also be explained, as well as the possible fields of application. Energy minimizing is a basic principle of physics; in other words, a system always strives to adopt a condition with the lowest possible energy. The formation of chemical bonds is an example of how this can take place. In a liquid, the cohesiveness (usually van-der-Waals- or Dipol-Dipol-interaction) attracts atoms and/or molecules of a similar type. Therefore, a liquid is energetically advantaged compared to a gas. Atoms and/or molecules on the surface of a liquid have fewer bonding partners and are therefore energetically disadvantaged in contrast to the corresponding particles within a liquid. Liquids, therefore, strive to minimize their surfaces, by forming the typical drop-shape. The surface energy is a measurement for the energy necessary to separate chemical bonds, when a new solid or liquid surface is created. It is defined as the energy

Figure 3-16: Octyl trialkoxysilane for the hydrophobicity of sol-gel-coating materials

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which must be invested in order to create the surface per unit of area. The SI-unit of surface energy is J/m², and the most common equation symbol is (gamma). Although the term “surface energy” is most commonly used, in the case of temperatures above absolute zero, the free energy of the surfaces must actually be considered. However, the difference is often minimal and can be neglected. The surface energy is always positive, because energy is required to separate bonds. Materials that have higher surface energy are easily covered by materials that have low surface energy (wetting), but the opposite does not hold true. The surface energy WOb is proportional to surface A. The equation applies: Equation 6

WOb =

A

The proportionality constant in Equation 6 refers to specific surface energy. One also refers to surface tension in liquids, and surface energy in solids, as well as interface energy and/or interface tension. The surface energies of both solids and liquids are crucial to the wetting of a surface. The wetting is the behavior of liquids when they come into contact with the surface of solids, or the formation of an interface liquid/solid. Wettability is the corresponding property. How heavily the liquid wets the surface is dependent upon what liquid is being used, what material the surface is made of and how it is structured, for ex., in regard to the roughness.

Wetting a surface with a liquid is characterized by the contact angle , which the liquid forms after a drop is applied to the corresponding surface. The correlation between the contact angle and the interface energies is indicated by Young’s equation (see Figure 3-17). Young’s equation (named after Thomas Young) makes a connection between the free surface energy S of a solid, the interface energy between the solid and a drop of liquid located thereupon, and the surface tension L of the liquid and the contact angle . The term “contact angle” refers to the angle that is formed between the drops of liquid on the surface of a solid, and the surface itself.

Figure 3-17: Contact angle of a liquid on a solid and the mathematical connection (Young’s equation) between the contact angle and the surface energies, or surface tensions of the participant phases [37]

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Figure 3-18: The contact angle as a measurement for the wetting behavior of water on a (solid) surface with various interfaces – or surface energies. Both sl as well as sg stand for the interface tension/energy between solid (coating) and liquid (water) as well as between solid (coating) and gas atmosphere (air).

The size of the contact angle between liquid and solid depends on the interaction between the substances on the contact area. The smaller this interaction is, the larger the contact angle. By determining the contact angle, certain properties of the solid’s surface, such as the surface energy, can be determined. A drop of liquid placed on a horizontal, level surface illustrates the wetting behavior and its classification. The smaller the contact angle is, the greater the wettability.

In order to evaluate if a drop spreads out on a surface, one compares the cohesiveness within the drop with the adhesiveness towards the surface. Should the liquid spread out on the surface in the form of a flat disc, or in other words should the adhesiveness greatly outweighs the cohesiveness (macroscopic contact angle non existent), one refers to complete wettability (Figure 3-18 lower right). In the case of a partial wettability, the liquid forms half-round domes, (contact angle less than 80°) which one can easily observe in the most common surfaces such as every-day window glass. Should the contact angle be greater than 80°, then the wettability is considered poor. Should the liquid shrink together to bead shape drop on the surface (contact angle greater than 140°) then there is no detectible wettability. Ideally, the contact angle should be 180°. In this case, the drop of liquid is touching the solid on only one point.

For water, it applies: the lower the surface energy sl, the poorer the wettability of the surface. Particularly in the case of water base paints, this leads to the possibility that one must reduce the surface tension of the water through the addition of additives (surfactants), or through elaborate pre-treatments, such as corona or flame activation, and charges must be applied on the surfaces to be coated for increasing the surface energy.

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If water is used as the liquid, one refers to the surface as being hydrophilic for a low contact angle (500 g/mole, so that the individual bonding agent molecules do not evaporate during the curing process between RT up to approx. 200 °C [201]. The inorganic crosslinking (formation of Si-O-Si-bridges) does not take place after the addition of water or mineral acids through hydrolysis and condensation, as is customary with silanes, but instead, it takes place by a direct crosslinking of Si-O-Si-units under the usage of specially developed catalysts (for example, metal complexes). This curing technology has the advantage that no hydrolysis and condensation processes take place, which in sol-gel systems often affect the storage stability, processability, and also the reproducibility, due to the water content. “Silixanes” distinguish themselves from sol-gel-systems particularly because they are storage-safe with up to nearly 100 % solids content and can be arbitrarily diluted with organic solvents. The first “silixanes” are currently available commercially as a bonding agent for lacquers with solvent content. The development is taking the direction of innovative powder-based paints. The special feature of this new bonding agent class is the combination of scratch resistance, the highest possible chemical resistance, and yet a high flexibility. The potential of the “silixanes” based on the coating properties of a test formula for plastic coatings will be described in the following. Within the scope of the basic examinations, one “silixane”-bonding agent with a urethane function and six alkoxy functions per monomer (see Figure 3-129) was used in a lacquer formula for the hard coating of plastic.

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Figure 3-129: Principal structural formula of a “silixane” with a urethane function, (R = CH3CH2-, CH3-)

For the production of the test formula, a bonding agent with 50 % solid (in butylglycol), a crosslinkage catalyzer on the basis of an Al-complex, and a process additive were added. A black plastic with the characterization of “Pocan” DP 7645 was used as a substrate for the coating. The coating solution was applied to one half of the substrate by means of flood-coating and subsequently cured in the drying chamber at 125 °C for 1 hour. The abrasion resistance was determined with an abrasion test device from the Erichsen company with an appropriate abrasion medium (abrasive fabric “3M Scotch Brite” No. 7448), see Figure 3-130. For the evaluation of the abrasion resistance, the degree of shine before and after 500 stress cycles to the coated and the uncoated side was compared (Figure 3-131). The uncoated side is visibly very severely scratched after the test. For the quantification of the abrasion resistance, the remaining shine percentage compared to the original shine of the surface was determined (see Table 3-17, page 142). The coated surface shows a small but noticeable loss of shine, however the remaining shine of the uncoated sample is only approx ~26 %. At the same time, the coating shows a very good chemical resistance against acids and alkaline solutions. An additional tested application is the coating of mineralbased substrates (for example natural stone,

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Figure 3-130: Abrasion Test device 494 Erichsen) and abrasion medium (abrasive fabric “3M Scotch Brite” No. 7448) for the determination of the abrasion resistance of the test formula

Figure 3-131: “Pocan” DP 7645 after 500 cycles abrasion test with abrasive fabric “3M Scotch Brite” No. 7448, left side uncoated, right side coated

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concrete) with “easy to clean” functionality for stain protection or for the increase of chemical resistance, and simultaneously, extremely high mechanical resistance, as shown in Figure 3-132. As shown in Figure 3-132, the “silixanes” have an outstanding stain resistance. This property is combined with excellent adhesion, abrasion resistance, and weathering stability. The necessary diffusion due to water vapor through the stone is not noticeably affected. “Silixanes” show unique property profile and make many new application possibilities available. The advantage these systems offer lies in the Table 3-17: Residual gloss (measuring angle 20°; DIN EN ISO 2813 bzw. DIN 67530) of coated and uncoated “Pocan DP 7645” after 500 cycles wear test with abrasive fabric “3M Scotch Brite” Nr. 7448 Substrate

Percentual residual gloss after wear test (with reference to 100 % starting gloss before mechanical damage to the surface)

“Pocan DP” 7645 (reference)

~ 26 %

“Pocan DP” 7645 with test coating

~ 98 %

Figure 3-132: Top picture: uncoated (left) and coated (right) concrete surfaces with different test substances before cleaning Bottom picture: uncoated (left) and coated (right) concrete surfaces with different test substances after cleaning with a damp cloth

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combination of these properties, which, in the case of sol-gel-systems, are not flexible enough for many applications, and in the case of organic coatings such as acrylate or polyurethane lacquers, are not abrasion resistant enough for many applications. In current studies, along with the further development for the powderlacquer industry, the integration of all kinds of nanoparticles in these systems is also being examined. “Silixane”-bonding agents are just beginning to get established in the market. Up to now, many important aspects of silane technology, and especially nanocoatings, have been demonstrated. Further applications will be discussed in the following. An important field of application for sol-gel- and nanocoatings is corrosion protection of metals, which will be explained in the following chapter. 3.6.5

Corrosion protection

The requirements for corrosion protection are just as diverse as the basic materials that need protection and the corresponding applications. The metals that are most common in practice are iron (steel), aluminum, zinc, copper and magnesium, in elementary form or as corresponding alloys. The only really corrosion resistant metals are gold and platinum, while even stainless steel can rust under corrosionpromoting conditions. In principle, all metals, depending on their intended use, must be protected from corrosion. In general, metals can be protected from corrosion by a likewise metallic coating or by a lacquer coating (generally referred to as organic in the lacquer industry). In principle, any metal, which is more corrosion resistant than the substrate metal, can serve as a corrosion protective coating. This does not mean that the coating must be from a more precious metal than the metal substrate. One of the most common methods to protect steel from corrosion is through a zinc coating applied by means of hot-dip galvanizing or electrogalvanizing. The Redox pair Zn/Zn2+ stands, just as Al/Al3+ and Mg/Mg2+, to the “left” of Fe/Fe2+ in the electrochemical series, and are less precious than iron. However, both zinc and also aluminum exposed to the atmosphere can be passivated by the formation of a very thin, practically pore-free oxide layer, and further oxidation can be inhibited in this way. As with the example of zinc, one advantage to using a less precious coating compared to the substrate is, that if the zinc coating is damaged and the steel surface is exposed, it remains protected to a certain extent, due to the sacrifice-function of zinc. Steel represents a cathode in this system, and therefore one refers to cathodic Figure 3-133: Dip galvanizing of steel corrosion protection. elements [202]

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But even a passivated metal surface such as zinc is worn away when exposed to the atmosphere, so that with outdoor exposure, the longevity of a zinc coating corresponds in years to its thickness in µm, which is normally in the range of approx. 5 to 50  m. If higher demands are made on the corrosion resistance, they must be coated with an additional conversion layer. In the past, this was often achieved by chromatizing. Now one attempts to replace the chromatizing process for environmental reasons and due to legal requirements. Basically, the properties of the bonding agent used (normally organic resins) are responsible for the properties of the protective coating. For the coating of a zinc over-coating, materials based on epoxy resin are often used, due to their good adhesion to zinc. These systems have a very good water resistance, but normally only a moderate to poor UV stability and weatherability, and a covering layer, often based on polyurethane or polyester, must be applied. In general, metals can also be protected from corrosion by coating directly, without metallic coverings. In addition to the coating, the pre-treatment is also of vital importance. The most common pre-treatment methods are the phosphatizing (on steel and zinc) and the chromatizing (on aluminum and zinc), which in the simplest case can be carried out by dipping in an aqueous phosphorous- or chromate solution. As a sole corrosion protection measure, phosphatizing and chromatizing are very limited in their effectiveness, and are therefore often implemented as a pre-treatment for an organic coating. With phosphatizing and chromatizing, fine crystalline, firmly adhesive, thin conversion layers are formed, which serve as an adhesion base for an outward coating. For an effective corrosion protection, up to four layers are applied to such conversion layer coating systems, of which each individual layer can easily reach a layer thickness of 50 to 100  m. With a growing standard of knowledge based on several decades, optimized systems, and their interactions, as well as specific sturdiness requirements, there is much to do in the field of corrosion protection, especially for heavy-duty corrosion protection as well as in the automobile industry. The demands and the expectations on chemical nanotechnology are correspondingly high. A general objective is to simplify the processes with nanomodified coatings and to reduce complexity of the multi-layer constructions by more efficient individual layers. There are approaches in which a part of the described pre-treatments or corrosion protection systems can be replaced or expanded by components or coatings from the chemical nanotechnology field. There are differing motivations for this, for example, in comparison to conventional methods, to obtain effective corrosion protection with low layer thicknesses or a simplified coating construction. Meanwhile, new substance approaches have established themselves, because they can compete on a cost level with existing systems, or because legislation forbids

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Figure 3-134: Schematic view of a SAM on a metal base, formed from a fluorinated chlorine silane (left, a) or from a fluoridated alkoxysilane (right, b)

existing methods, such as the EU’s old car guidelines, which prohibit methods involving chrome (VI) for new cars by the end of 2007, due to cancer-causing effects and the ecological dangers of bonds containing chrome. 3.6.5.1   Self assembling monolayers (SAM) One use of coatings in the nanorange is provided by the so-called SAMs (self assembling monolayers). These are used for temporary corrosion protection, for example, so that moisture is kept away from the interface to metal by a hydrophobicity of the surface (see Figure 3-134). As shown in Figure 3-134, the fluorine silane initially reacts with free hydroxyl groups, which are found on the metal surface. In a second step, the silanes crosslink further, under the influence of moisture, to a three-dimensional siloxane network. The organic fluorine side chains ideally place themselves perpendicular to the metal base, while the silane heads dock directly on the metal (as a monolayer). A further use for SAM-technology is alternative pre-treatment methods. Largely silane-free methods are discussed in the literature, by which the metal component needing protection is dipped in a solution of purely organic monomers with specific anchor groups (for example, phosphonic acids, which have a high affinity to the metal surface), whereas through the monomer`s self-ordering, a monomolecular, firmly adhering coating is formed, analogous to the structures presented in Figure 3-134. Along with the anchor group, the monomers also contain a spacer as well as a head group, which is oriented “away from the metal” and which can be crosslinked to a “two-dimensional” polymer layer, as in the case of thiophene groups with neighboring groups. They serve as adhesion agents for an organic coating. These

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Figure 3-135: Schematic presentation of the construction of a sol-gel corrosion protective coating and its adhesion to a metal surface

systems have been examined closely in recent years, and offer a very interesting and cost-efficient alternative to phospatizing or chromatizing, due to the low layer thickness [203]. Products suitable for series production for aluminum wheels are already available on the market as a replacement for chromatizing aluminum [204]. A further example is very thin silane primer coats, for example, based on amino silanes, which are used as adhesion primers for powder lacquers [205]. 3.6.5.2   Nanoparticle-filled siloxane coatings As a fundamental principle of nanotechnology, the sol-gel-process offers the lacquer chemist a multitude of possibilities for corrosion protection, to create new materials with inorganic and organic components which are connected on the molecular level. Hydrolyzed silanes and their condensates, if they are not completely condensated, have a large number of reactive silanol (Si-OH)-groups, which can bond covalently with metal-OH-groups existing on the metal surfaces. Nanoparticles can serve either as filler or as a depot for corrosion-inhibiting substances, as shown in Figure 3-135. As one can recognize from Figure 3-135, through the firm adhesion and additional film-forming properties of the sol-gel-coating, the metal surface is sealed and isolated from corrosion-enhancing media (moisture, etc.). In principle, every sol-gellayer improves the corrosion resistance of a metal in comparison to its uncoated condition. In order to obtain adequate corrosion protection, it is a prerequisite that the protective layer show outstanding adhesion. Epoxy-modified silanes are principally suitable for this, such as glycidyloxypropyl triethoxysilane (GPTES), which is described in Chapter 3.6.1. With appropriate synthesis management, the alkoxy groups are separated through hydrolysis under the formation of silanol groups, which form the “bridges” to the metal surface. Under base catalysis, the epoxy ring opens itself and links with further epoxy functions to form a polyether framework. A crosslinking can also occur with purely organic reaction partners such as bisphenolic diols. It has been determined that such coatings, starting at a layer thickness of approx. 3  m, show outstanding

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corrosion protective properties, especially on light metals such as aluminum and magnesium alloys (Figure 3-136).

The coated test plate seen in Figure 3-136 shows no corrosion after 1,000 hours salt spray test, including the scratched portion. No corrosion creeping took place. One can explain these results by the formation of a stable Si-O-Al-bond between the substrate and the protective coating, which has less energy and is therefore more stable than the corresponding corrosion products of the aluminum alloy.

Figure 3-136: Aluminum (AlMn0,5Mg0,5) after 1000 h salt-spray test according to DIN 50021; left uncoated, right coated with a 2 µm thick nanocomposite layer based on SiO2 with epoxy modification (GPTES)

If the layer, along with an adhesion-improving effect on an outer coating, should also show a corrosion protective effect on a nonpassivated metal surface such as steel, then it must also possess a high impermeability. When coating steel with nanoparticulate siloxane coatings, in contrast to aluminum, one must keep in mind that the corrosion products of iron are energetically favored compared to the corresponding Si-O-Febonds. Rust formation results on flawed Figure 3-137: Stainless steel lamp post sections or damaged spots that are not with (left) and without (right) nanocomposite-coating after 300 h salt protected by the density of the passivation spray test according to DIN 50021 layer. The effects are adequate for non-rusting or slightly rusting steels, which are, however, not adequately inert for certain applications. A corrosion protective coating of only 1 to 3  m for stainless steel based on siloxane serves as an example, which can protect steel against corrosion on construction components in the outdoor range, even in atmospheres containing salt (Figure 3-137). In addition to corrosion protection, the coating suitable for outdoor use, shown here, also has an anti-fingerprint – and ETC (“easy to clean”)-function. In addition to the coating of individual components, a coating according to the coil coating-method (band coating) is also possible for the application of nanocomposite coatings. Such a siloxane coating without active corrosion protective components is usually suitable only for the temporary corrosion protection of mild steel. With appropriate coating compositions without special pre-treatments, one can prohibit red-rust formation with a 2 to 3  m layer without additional over-coatings in the salt spray

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test without damage to the coating over a 100 hour period. Active corrosion protection can be achieved through the integration of zinc pigments. 3.6.5.3   Cathodic corrosion protection with nanoparticulate approaches Zinc coverings that are galvanically deposited or applied by means of the molten dip method belong to today`s standard for corrosion protection of normal steel. These overcoatings have the disadvantage that the zinc is quickly covered with white-rust when subjected to weathering. Therefore, in order to achieve long-term corrosion protection, very high layer thicknesses are applied. Should one wish to avoid this, then additional over-coatings must be applied in order to protect the zinc. By mixing zinc-pigments into the siloxane coatings, one has the problem that on the one hand, the SiO2 is very surface-active, and on the other hand, it is a non-conductor. Therefore, one can easily apply such systems as coating for metal, but the active corrosion protection is largely forfeited due to the missing electrical connection of the pigments amongst themselves or to the substrate. A well-known example for this is the zinc dust paints that have been used for several decades, which are based on TEOS (tetraethoxysilane)-hydrolyzates with a high filling-degree of zinc dust. The nanotechnological approach to the production of active zinc coatings is to replace the non-conductor SiO2 as a bonding agent of the pigments with a semiconductor TiO2. Figure 3-138 shows the construction of an active corrosion protection coating containing zinc. The semi-conductor (in most cases TiO2) has several functions. During synthesis, the titanium oxide is adsorbed on the surface of the zinc particles and already protects them in the coating solution. The layer thickness on each zinc particle is only a very few nanometers. After application and curing, these coatings bond the reactive Ti-OHgroups to a dense network. Since every particle is covered with a layer of TiO2, the white-rust formation is drastically reduced, while through the semi-conducting properties of the TiO2, sufficient contact is maintained with the individual zinc pigments amongst themselves and to the substrate (Figure 3-139). Figure 3-138: Schematic presentation for the construction of an active corrosion protection coating based on zinc pigments which are embedded in an inorganic semi-conducting material

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Figure 3-139 shows the outstanding properties of a 5 µm zinc titanium dioxide-coating compared to an approx. 30 µm galvanized zinc-coated plate, that after 1,000 hours salt spray test (ISO 9227) already showed very severe white-rust formation. An uncoated

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Figure 3-139: Comparison of coated steel plates after 1,000 h salt spray test according to ISO 9227, left: zinc titanium dioxide-coating, middle: without coating, right: galvanized zinc-coated steel

plate is completely rusted after this exposure. The objective of this development is to substitute the over-coatings by a rise in the corrosion protective effect of the thin zinc titanium dioxide-coatings. An interesting special use for nanocoatings on steel comes from the field of hightemperature corrosion protection. This coating, to be explained in the following chapter, which protects steel from the formation of scale, is an outstanding example for the combination of a nanotechnological approach with the principles of conventional lacquer chemistry. 3.6.6

Protective coating against scaling for steel during hot stamping – nanotechnology combined with lacquer chemistry

An innovative coating opens further possibilities for the cold- and hot stamping of steel plates. Considering the current high security requirements, load-bearing components in the automobile industry are being constructed increasingly by selected highly stable and extremely stable types of steel. With manganese boron steel (22MnB5), firmness levels of up to 1,650 MPa can be achieved through hot stamping (press curing), compared to 1,100 MPa in the case of cold shaping with highly-firm car-body steel. For the press curing process, the steel is austenitized at 950 °C by heating the corresponding plates. The plates are subsequently placed into the press form and shaped. The form component is quenched in the form to temperatures between 100 and 200 °C. A martenistic structure and therefore a high-strength building component is created. A well-known problem, which occurs here as well as with other high-temperature processes with low-alloy steel, is the scaling (high-temperature oxidation) of the

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Figure 3-140: Principal of the press curing of steel plates

steel surface. Scales are formed within just a few seconds, as soon as the hot surface (over 900 °C) comes into contact with atmospheric oxygen. During the heat-up phase, which can be done under protective gas with the corresponding constructive alterations and substantial financial outlay, contact with the surrounding air is ultimately unavoidable, when the plate or component is transferred into the press form. Figure 3-141 shows the extent of the scale formation on a 22MnB5 steel plate after 10 min annealing at 950 °C.

Figure 3-141: Scales on 22MnB5-steel plate after 10 min annealing at 950 °C under air atmosphere

The resulting scale layer is rough and brittle, flakes off extensively, and offers no basis for consecutive processes such as welding and cataphoretic painting. By using such scaled steel, the expensive forms were damaged in a short time and had to be cleaned after every hot-stamped building compo-

Figure 3-142: Schematic process of indirect press curing

Figure 3-143: Model of a flexible matrix from inorganic/organic nanostructures filled with microscale aluminum particles

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nent. Production of adequate quantities of components for series production was severely hindered. Because the steel can only receive limited protection from scaling (as described) by constructive measures (protective gas), the protection must occur right on the steel surface, or by means of a protective coating. State-of-the-art hot-dip aluminized steel types are available, to which the coil has applied an approx. 25  m thick aluminium silicon-alloy, which protects the steel from scaling during heat forming. However, for reasons of practicality and for building components of a certain size and complex shape, one increasingly tends to process the components in two steps, namely a cold-shaping with a subsequent heat-re-shaping (indirect press curing). Figure 3-142 demonstrates the principal of indirect press curing. As shown in Figure 3-142, indirect press curing involves two steps. In the first step, a building component is preformed from a plate by means of cold shaping, and in a second step, the component is heated to 950 °C and then given its final shape by being placed in a cooled press form. Up until recently, no protective coating existed which was suitable for such a combination method. A shapable protective lacquer against the scaling of steel has been developed for indirect press curing based on a nanotechnological approach [206]. The coating material is based on an inorganic/organic bonding agent, that is filled with microscale aluminum particles (Figure 3-143).

Figure 3-144: Left, above: Coated plate is placed in an oven heated to 950 °C, right above,. red glowing plate after 10 min at 950 °C without protective gas, left below, uncoated back scaled, right below coating intact

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Figure 3-145: Left: steel coil coated with protective lacquer; right: form cured tunnel piece, left without, right with protective lacquer

As shown in Figure 3-143, the aluminum particles are embedded in the flexible inorganic/organic network. The attempted annealing of coated plates (formed after coating) shows the coating’s effectiveness against scaling (Figure 3-144). As demonstrated in Figure 3-144, upon removal from the annealing oven, one can observe scaling on the black coloration of the uncoated stripe, whereas the coated areas appeared to glow red, and after cooling, showed a firmly adhering smooth surface. During the annealing, the temperature resistant components of the coating react with the steel surface and form an oxidic protective coating, which contains elements of iron, aluminum, silicon and oxygen [207–210]. The coating takes place directly on steel coils and is used for the mass production of geometrically complex shaped car-body components (Figure 3-145). As is evident in Figure 3-145, the surface of the building components with protective lacquer are more homogenous. The protective lacquer facilitates the problemfree application of steel materials with cold-shaping and with press cured shaping, and is already being used for several building components and vehicles. These types of protective coatings against scaling, which can also be applied by means of spray application, can also be used for forging or other high-temperature processes with steel.

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Outlook

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153

Outlook

We have introduced you to the complex interactions of chemical nanotechnology by using the example of silane technology. Silane technology offers the possibility to combine inorganic and organic structure units. Based on such inorganic/organic bridge molecules, so-called silanes and/or organosilanes, the multitude of combination possibilities were presented with regard to six reaction principles. As a start reaction, the sol-gel-process and therefore also the hydrolysis and condensation of silanes to siloxanes facilitates the production of thin layers or silicate nanoparticles. In the least complicated case, the organic sidechain can serve as a network modifier and therefore facilitate the flexibilization, whereas the attribute profile of the resulting bonds can be very similar to silicones, without having the typical disadvantages of silicone chemistry. Fundamental knowledge and reaction principles of glass chemistry can be used to modify the inorganic network and consequently achieve an increase in chemical resistance or a higher degree of hardness. If one extends the organic sidechain on the silane by means of a simple hydrocarbon chain (> 8 CH2-) or uses a fluorinated species or polyether chain, one then gets molecules that are similar to the surfactant, which affect the surface when used in lacquers, and particularly in sol-gel-systems. The surface energy is modified, and therefore the attribute profile can be customized between “easy to clean” to hydrophilic or anti-fog. Nanoparticles can be occupied via the inorganic side of the “bridge molecules” (silane) through a so-called silanization reaction with covalently bound organic structure units. This silanization leads to the stabilization of the nanoparticles against (re-) agglomeration and often first splits remaining agglomerate (with commercial nanoparticles-dispersions or -powders) into their primary particle size. Through this surface modification, the generally inorganic nanoparticle interface becomes compatible with the surrounding organic (in the case of paints and lacquers) coating matrix. If the utilized silanes can react to themselves or with the surrounding matrix, they are referred to as network formers. Through this, further application possibilities (polymerization- or addition-reactions) present themselves, which facilitates the homogenous and stable integration into reactive lacquer and paint systems. The respective production principles and surface modifications can be adjusted to meet the application needs. Stefan Sepeur: Nanotechnology © Copyright 2008 by Vincentz Network, Hannover, Germany

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Outlook

By combining all the described reaction principles, silane- and nanotechnology have the ability to create matrices, which by means of glass-like structures, can firmly bond ceramic solid particles into an organic polymer network. In doing so, the surface energy and structure can also be adjusted. A world of possibilities opens up, which reveals previously unobtainable attribute profiles. Of course, the field of chemical nanotechnology encompasses other areas such as the creation and processing of organic nanopolymer structures, bulk materials and through this, plastic modifications, impregnations, biological and medicinal applications or metallic particles. The perspectives are difficult to express in one sentence. But in each area, whether its scratch resistant lacquer, catalytically active coatings, self-cleaning surfaces, corrosion protection materials etc., the development has only just begun to pick up direction and speed. Commercial lacquer chemistry is increasingly open to new materials, while the development in the area of new materials focuses increasingly on usability with commercial technologies. Much ground will be covered in the next few years due to this convergence, and we hope this book brings the world of silane and chemical nanotechnology somewhat closer. This book should present the most important reaction possibilities for the field of coating materials. It should give encouragement to new viewpoints for research and solution possibilities for industrial application. Many of the noted systems and materials are patented methods and can not be simply reproduced. One should carefully look into the patent literature before any commercial use of these technologies. Because we can only touch the surface of each individual theme, we have included a thorough bibliography, so that the reader can easily access more detailed information, if desired. We also happily encourage our readers to contact us personally in the case of specific questions.

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Literature

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Literature

General literature Neal Stephenson: Diamond Age (1996) – dt. Diamond Age – Die Grenzwelt (1996) Neal Stephenson: Snow Crash (1991) Marcus Hammerschmitt: Der Zensor (2001) Arthur C. Clarke: Fountains of Paradise (1979) – dt. Fahrstuhl zu den Sternen; siehe auch Weltraumlift Michael Crichton: Prey (2002) – dt. Beute Greg Bear: Queen of Angels (1990) – dt. Königin der Engel (1993) Greg Bear: Slant (1997) Kathleen Ann Goonan: Queen City Jazz (1994) Kathleen Ann Goonan: Mississippi Blues (1997) Kathleen Ann Goonan: Crescent City Rapsody (2000) Kathleen Ann Goonan: Light Music (2002) Peter F. Hamilton: The Nano Flower (1995) – dt. Mindstar, Die Nano-Blume (1999) John Robert Marlow: Nano (2004) Britt D. Gillette: Conquest of Paradise (2003) Stanisław Lem: Wizja Lokalna (1982) – dt. Lokaltermin (1985) Stanisław Lem: Pokój na ziemi (1986) – dt. Der Flop (1986), Frieden auf Erden (1988) Kevin J. Anderson & Doug Beason: Assemblers of Infinity (1993) Jack Dann & Gardner R. Dozois eds: Nanotech (Anthology) (1998) Elton Elliott ed: Nanodreams (1995) Michael Flynn: Nanotech Chronicles (1991) Bart Kosko: Nanotime (1997) Nancy Kress: Beggars and Choosers (1994) Wil McCarthy: Bloom (1998) Linda Nagata: The Bohr Maker (1995) Linda Nagata: Tech Heaven (1995) Walter Jon Williams: Aristoi (1992)

Technical literature G. Schmid (Ed.): Nanoparticles – From Theory to Application; Dez 2003; Wiley-VCH Uwe Hartmann: Faszination Nanotechnologie. Spektrum Akademischer Verlag. 2005 K. Eric Drexler: Nanosystems (Kapitel 1 u. 2, HTML) K. Eric Drexler: Engines of Creation K. Eric Drexler: Unbounding the Future Robert A. Freitas: Nanomedicine (Vol. I als HTML) Douglas Mulhall: Our Molecular Future Stefan Sepeur: Nanotechnology © Copyright 2008 by Vincentz Network, Hannover, Germany

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Nadrain C. Seeman: Karriere für die Doppelhelix, Spektrum der Wissenschaft, Januar 2005 Bundestagsdrucksache “Stand und Entwicklung der Nanotechnologie in Deutschland”, BTDrs. 14/5443 vom 28. 2. 2001 Nanofair 2004 New Ideas for Industry – International Symposium VDI Bericht 1839, 2004 Niels Boeing: Nano ?! – Die Technik des 21. Jahrhunderts; 2004;

Technical literature 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

C.J. Brinker, G.W. Scherer Sol-Gel Science: The Physics and Chemistry of Sol-Gel Processing: The Physics and Chemistry of Sol-gel Processing, Academic Press Inc., 1990 C.J. Brinker, J. Non-Cryst. Solids 100 (1988), 31 H. Reuter, Adv. Mater. 3 (1990) 259 C.J. Brinker, G.W. Scherer, J. Non-Cryst. Solids 70 (1985) 301 B.M. Novac, Adv. Mater. 5 (6) (1993) 422 T.N.M. Bernards, M.J. von Bommel, A.H. Boonstra, J. Non-Cryst. Solids 134 (1991)1 A.F. Wright and J. Dupuy (Hrsg.), Martinus Nijhoff Publischers, Dordrecht, Boston, Lancaster, 1985, 263 H. Schmidt,A. Kaiser, H. Patzelt,H. Scholze, J. Phys. 43 (1982), 275 H. Schmidt, A. Kaiser, Glastechn. Ber. 54 (1981), 338 J.C. Brinker, G.W. Scherer (Hrsg.), Sol-gel Science (1990), Academic Press, London S. Sakka; Mat.Res. Soc.Symp.Proc. 32, 91 (1984) S. Sakka; Y. Tanaka und T. Kokubo; J. Non-Cryst. Solids 82, 24 (1986) M. Ebelmen, Ann. Chim. Phys. 16 (1846) 129 M. Ebelmen, Ann. Chim. Phys. 25 (1847) 854 158 T. Graham, J. Chem. Soc. 17 (1864) 289 R.K. Iler, The Chemistry of Silica, Wiley, New York 1955, 1979 L.L. Hench, J.K. West Chem. Rev. 90 (1990) 33 R.J.P. Corriu, D. Leclerq, A. Vioux, M. Pauthe, J. Phalippou, Ultrastructure Processing of Advanced Ceramics, D.J. Mackenzie, D.R. Ulrich (Hrsg,), Wiley, New York 1988, S.113 C.J. Brinker, G.W. Scherer, Sol-Gel Science, Academic Press, San Diego 1990 J. Fricke, Aerogels, Vol.6, Springer Proc. Phys., Springer-Verlag, Heidelberg 1986 E. Matjevic, Chem. Mater. 5 (1993) 412 W. Stöber, A. Fink, E. Bohn, J. Colloid Polym. Sci. 26 (1968) 62 J.T.G. Overbeek, Adv. Coll. Interf. Sci. 15 (1982) 251, 16 (1982) 17 A.K. van Helden, J.W. Jansen, A. Vrij, J. Colloid Interface Sci. 81 (1981) 354 160 H. Schmidt and B. Seiferling, Mat.Res.Soc.Symp.Proc.Vol. 73 (1986), 739 Peter F. James: The gel to glass transition: Chemical and microstruktural evolution, J. Non-Cryst. Sol. 100 (1988) 93 –114 R. Kasemann, S. Brück and H. Schmidt: in Proceedings 2nd Eurogel Conf., June 2–5 (1991), Saarbrücken H. Schmidt, H. Scholze, A. Kaiser, J. Non-Cryst. Solids 63 (1984) 1 E.R. Pohl, F.D. Osterholz, in: Molecular Characterization of Composite Interfaces: Hrsg.: H. Ishida, G. Kumar: Plenum, New York 1985, 151 K.J. McNeil, J.A. Ciaprio, D.A. Walsh, R.F. Pratt, J. Am. Soc. 102 (1980) 1859

VIN Sepeur engl 05 AM.indd 156

21.04.2008 14:26:20 Uhr

Literature

31 32

33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51

52 53 54

157

Karin Piana, Dissertation “Gel”, Bayrische Julius-Maximilians-Universität Würzburg, Würzburg 1993 H. Schmidt, G. Philipp, B. Seiferling, K. Deichmann, “Development of organic-inorganic hard coatings by the sol-gel process”, in Ultrastructure processing of advanced ceramics [Proceedings of the 3rd Int. Conf. On Ultrastructure Processing of Ceramics, Glass and Composites], 23–27 Februar 1987, San Diego, Calif Horst Scholze, Glas Natur, Struktur, Eigenschaften, Springer-Verlag, Heidelberg (1988), 3. Auflage NANO-X GmbH, DE 10 2005 027 789 A1, “Alkalistabile Sol-Gel-Beschichtung”, 21.12. 2006 NANO-X GmbH, WO 2006 /133677, “Alkali-stable Sol-Gel-Coating”, 21.12. 2006 Forschungszentrum in Karlsruhe, http://www.fzk.de Quelle: www.kruess.de Eingetragene Marke Du Pont: “Teflon AF” P.R. Resnick: Polymer Preprints, 31, 312 (1990) DE 19917367 A1, “Verfahren zur Herstellung von Überzuegen auf Basis fluorhaltiger Kondensate”, 19.10. 2000 INM, Saarbrücken, EP 01177264 B1, “Method for producing coatings based on condensates containing fluorine”, 18.12. 2002 INM, Saarbrücken, DE 04118184 A1, “Beschichtungszusammensetzungen auf der Basis von fluorhaltigen anorganischen Polykondensaten, deren Herstellung und deren Verwendung”, 10.12.1992 M. Mennig, G. Jonschker, H. Schmidt: Sol-Gel Derived Thick Coatings and Their Thermomechanical and Optical Properties, Mackenzie J. D., Ed. Bellingham: SPIEINT Soc. Optical Engineering, Vol 1758 pp, 125–134, 1992 (BX27C) R. Kasemann, C. Bersin, H. Schmidt: Proc.1.st. Int. Conf. on Application and Commercialisation of Sol-Gel Processing, Saarbrücken, October 10–13, 1993, Trans Tech Publication Ltd., Aldermannsdorf/ Switzerland R. Kasemann, S Brück, H. Schmidt: 66. Glastechnische Tagung, 25–27 Mai (1992) Fulda, 28 NANO-X GmbH, WO 002003014232A1, “Material for producing abrasion-proof, hydrophobic and/or olephobic coatings”, 20. 2. 2003 Quelle: NANO4YOU GmbH, Bexbach, www.nano4you.com Quelle: http://www.americanstandard-us.com/Innovations/everclean/Everclean.aspx Quelle: http://de.wikipedia.org/wiki/Bild:Tropaeolum-majus%28lotus-oben%29.jpg Z. Cerman, A.K. Stosch, W. Barthlott, “Der “Lotus-Effekt”. Selbstreinigende Oberflächen und ihre Übertragung in die Technik”, Biologie in unserer Zeit 5, 290–296 (2004) W. Barthlott, C. Neinhuis, “Der Lotus-Effekt: biologische Grundlagenforschung und die Entwicklung neuer Werkstoffe” in: A. Gleich, “Bionik. Ökologische Technik nach dem Vorbild der Natur?”, 2. Auflage, B. G. Teubner Stuttgart Leipzig Wiesbaden, S. 189–203 (2001) W. Barthlott, Nees-Institut für Biodiversität der Pflanzen, Universität Bonn W. Barthlott, Europäisches Patent 95927720.3/0772514 (1998): “Selbstreinigende Oberflächen von Gegenständen sowie Verfahren zur Herstellung derselben” Werner Nachtigall, Natur macht erfinderisch, Ravensburger Buchverlag; Auflage: 1 (2007)

VIN Sepeur engl 05 AM.indd 157

21.04.2008 14:26:20 Uhr

158 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82

Literature

Werner Nachtigall, Bionik - Grundlagen und Beispiele für Ingenieure und Naturwissenschaftler. Berlin: Springer Verlag, 2. Aufl. 2002 W. Barthlott, Scanning electron microscopy of the epidermal surface in plants. In: Scanning electron microscopy in taxonomy and functional morphology (Claugher, D., Eds.). Clarendon Press, Oxford, 69 – 94, 1990 http://de.wikipedia.org/wiki/Bild:LotusEffekt1.jpg http://de.wikipedia.org/wiki/Bild:LotusEffekt2mq.jpg S. Sepeur, Innovative surfaces for the ceramic industry, Zeitschrift Ziegelindustrie International Vol 57 No. 1– 2 S. 19 (2001) Quelle: Sto AG, Stühlingen, http://www.lotusan.de NANO-X GmbH & Genthe-X-Coatings, EP 01448719B2, “Beschichtung zur dauerhaften Hydrophilierung von Oberflächen und deren Verwendung – Coating for permanently hydrophilizing surfaces and the use thereof”, 25. 8. 2004 NANO-X GmbH, DE 10 2006 023 375.1– 43, “Beschichtungsmaterial KST-System”, 22.11. 2007 M. Oswald, A. Rößler, F. Menzel, K. Deller, “Praxisnahe Charakterisierung von Aerosil” www2.sivento.de Fa. Degussa, Schriftenreihe Pigmente Nr. 11 – Grundlagen von AEROSIL Fa. Degussa, Schriftenreihe Pigmente Nr. 16 – Untersuchungsmethoden für synthetische Kieselsäuren und Silikate S. H. Bell, V. T. Crowl: Dispersion of Powders in Liquids, G. D. Parfitt, ed., John Wiley and Sons, New York 1973 H. P. Böhm: Angew. Chem. 12, 617– 652 (1966) J. C. Bolger: Acid -Base Interactions between Oxid Surfaces and Polar Organic Compounds, pp. 3-18 in Adhesion Aspects of Polymeric Coatings, Edited by K. L. Mittal, Plenum Press, New York, 1983 W. H. Meyer, J. Böhnlein-Mauß, W.Sigmund, G.Wegner: Adv. Mater. 4 (1992), 73 C.H.M. Hofmann-Caris in: “First European Workshop on Hydrid Organic-Inorganic Materials”, Chateau de Bierville (Frankreich), 8–10 November 1993 H. Schmidt, Mat. res. Soc. Symo. Proc. 274 (1992) 121 J. Cesarano, I.A. Aksay, J. Am. Ceram. Soc. 71 (4) (1988) 250 P. Ney, “Zetapotentiale und Flotierbarkeit von Minerialien”, Springer Verlag Wien (1973) Quelle: Institut für Neue Materialien, Saarbrücken, www.inm-gmbh.de Quelle: http://www.reclot.de/kapitel/20miner.htm Quelle: http://www.fkp.physik.tu darmstadt.de/fprakt/roentgenstruktur/roentgen.doc Quelle:http://lamp.tugraz.ac.at/~nanoanal/de/sub_methoden.php?cms_id=M15# bilder Quelle: http://en.wikipedia.org/wiki/BET_theory D. W. Schaefer und K. D. Keefer, Mat. Res. Soc. Symp. Proc. Vol. 32, Elsevier Science Publishing Co., 1984 Quelle: inomat GmbH, Bexbach, http://www.inomat.de/ Department of Geological Sciences, Mineral Structures Laboratory, University of Colorado, Boulder, CO 80309 (USA), http://ruby.colorado.edu/~smyth/min/tio2.html Quelle: http://www.wdr.de/tv/quarks/sendungsbeitraege/2002/0806/006nano.jsp sowie Beiersdorf AG, Hamburg, www.beiersdorf.de

VIN Sepeur engl 05 AM.indd 158

21.04.2008 14:26:20 Uhr

Literature

83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109

159

A. Fujishima, T. N. Rao, D. A. Tryk, Journal of Photochemistry and Photobiology C: Photochemistry Reviews 1 (2000) 1– 21 St. Gobain, Europäische Patentschrift EP 0850204 B1, “Substrat mit photokatalytischer Beschichtung” St. Gobain, Europäische Patentschrift EP 01132351 B1, “Substrat mit photokatalytischer Beschichtung” Pilkington, Europäische Patentanmeldung EP 01608793 A1, “Titandioxid-Beschichtungen” Pilkington, Europäische Patentschrift EP 0944557 B1, “Verfahren zur Abscheidung von Beschichtungen aus Zinnoxid und Titanoxid auf Flachglas und so beschichtetes Glas” Quelle: Deutsche Steinzeug, KerAion Hydrotec, www.deutsche-steinzeug.de Quelle: St. Gobain, SGG Bioclean, www.saint-gobain-glass.com Quelle: Pilkington Aktiv, www.pilkington.com NANO-X GmbH, Patent DE 101 58 433.4-43, “Beschichtung” W. Barthlott, Europäisches Patent 95927720.3/0772514 (1998): “Selbstreinigende Oberflächen von Gegenständen sowie Verfahren zur Herstellung derselben”, Erlus Baustoffwerke, Deutsches Patent DE 19958321 A1 “Verfahren zur Erzeugung einer Selbstreinigungseigenschaft von keramischen Oberflächen” Quelle: http://www.city-filter.de/home.php Quelle: http://www.itn-nanovation.com/main.asp?page=produkte&subpage=BU1_ Kata_Ofen M. Cheng Nanostructures Science 303 (2004) 661 155 b F. Bauer, V. Sauerland, E. Hartmann Quelle http://www.me.vt.edu/nrylander/home/home.html Quelle http://en.wikipedia.org/wiki/Image:Types_of_Carbon_Nanotubes.png Quelle http://www.nano-lab.com/carbonnanotubes.html Quelle http://www.nanotech-now.com/Art_Gallery/LiftPort.htm N. S. Plachkov, Dissertation ”Bakterizid-Ausrüstung von Kunststoffen mittels Silberund Silberlegierungs-Nanopartikeln” Universität des Saarlandes 2006 G. v. Francois, P. Karrer, Über den enzymatischen Abbau von Chitin II, Acta Helevetica Acta 12 (1929), 5. 986 –993. E. Schollmeyer, D. Knittel, Chitosan und seine Derivate für die Textilveredlung, Textilveredlung, 33 (1998), 5. 67–71. R. H. Wittke, Dissertation “Darstellung und Funktionalisierung von Polymeroberflächen” Universität Duisburg-Essen (2005) M. Kluke, Dissertation “Synthese und Charakterisierung anorganisch-organischer Beschichtungsmaterialien auf der Basis von 3-Isocyanatopropyltriethoxysilan” Universität des Saarlandes, Saarbrücken 2005 Quelle: http://en.wikipedia.org/wiki/Ormosil Sol-Gel Science and Technology, M.A. Aegerter, M. Jaffelicce, D.F. Souza, E.D. Zanotto (Hrsg.), World Scientific Publishing Co. PTE Ltd. Singnapore 1989,432 Bayer Walter, Lehrbuch der organischen Chemie, S. Hirzel Verlag, 1988 W. Glaubitt, Diplomarbeit: “Quantitative Bestimmung von Epoxid- und Glykolgruppen in organisch modifizierten Silicaten” Universität Würzburg, August 1985

VIN Sepeur engl 05 AM.indd 159

21.04.2008 14:26:21 Uhr

160

Literature

110 S. Arnberg-Schwab, E. Arpac, W. Glaubitt, K. Rose, G. Schottner, U. Schubert, in: High Performance Ceramic films and coatings; Hrsg.: P. Vincenzini: Elsevier Science Publisher B.V., 1991 111 H. Schirra, Diplomarbeit: “Grundlegende Untersuchungen der Reaktion von y-GlucidOxypropyltrimethoxysilan mit alipatischen und aromatischen Diolen”, Universität des Saarlandes, Saarbrücken 1995 112 Dalibor Horst, Binders for Coatings, Deutsche Offenlegungsschrift DE 3545893 A1 113 Tsuneta, Kanzuyoshi; Nagai, Masanori; Ogawa, Osamu; Tanida, Osamu; Corrosion-resistant coating composition based on bisphenol A/ bisphenol-F epoxy resins, Europäische Patentschrift, EP 420063 A2 910403 114 A.J. Broadbent, J Crozier, P. Mc. Donald, Adv. Cog. Eng. (1997), 42A, 161-168 115 Susan R. Howe, L. Brondinsky, R.S. Lion, J. Coat. Technol. (1998), 70 (877), 69-74 116 J.E. Biles, T.P. Mc Neal, T.H. Begley, J. Agric. Food Chem (1997), 45 (12), 4697–4700 117 S. Sepeur, Dissertation “Entwicklung von abriebfesten, wasser- und chemikalien­ beständigen Beschichtungsmaterialien auf Basis des Sol-Gel-Prozesses für Poly­ methylmethacrylat (PMMA) und verfahrenstechnische Anpassung der Systeme an einen Vakuumtiefziehprozess”, Universität des Saarlandes, Saarbrücken (2001) 118 S. Sepeur, Diplomarbeit, Universität des Saarlandes, Saarbrücken (1995) 119 M. Laval, Diplomarbeit, Universität des Saarlandes, Saarbrücken (1996) 120 Merck IR-Atlas 121 K. Buchner, R. Kasemann: Proc.1.st. Int. Conf. on Application and Commercialisation of Sol-Gel Processing, Saarbrücken, October 10–13, 1993, Trans Tech Publication Ltd., Aldermannsdorf/ Switzerland 122 H. P. Böhm, G.. Kämpf: Z. phys. Chem. Neue Folge 23 (1960), 257 123 H. B. Böhm, M.Schneider: Z. anorg. allg. Chem. 301 (1959), 326 124 O. Glemser, G.Rieck: Angew. Chem. 68, 182 (1956) 125 J. B. Peri, R. B. Hannan: J. physic. Chem. 64, 1526 (1960) 126 PPG Industries, Patentanmeldung EP 1 204 701 B1 (2005) 127 Quelle: http://www.innovationspreis.com/teilnehmer/teiln2004/short57.html 128 R. Kasemann, H. Schmidt, E. Wintrich, New type of a sol-gel derived inorganic-organic nanocomposite, In: Proceedings 1994 MRS Spring Meeting, Symposium “Better Ceramics Through Chemistry VI”, April 1994, San Fransisco/USA, Mat. Res. Soc. Symp. Proc. 346 (1994) 129 Patentanmeldung DE 43 38 361 A1, 10.11.93 130 R. Kasemann, H. Schmidt: Proc. First European Workshop on Hybrid Organic-Inorganic Materials, Château de Bierville/France, November 1993 131 E. Geiter, Dissertation, Universität des Saarlandes, Saarbrücken (1997) 132 Winkler, Becker, Rietz, Krug, Mennig, Gerhard, Mohr, Jahrestätigkeitsbericht Institut für Neue Materialien 1994, S. 122 133 C. Dittfurth, S. Sepeur, R.P. Winkler, H. Schmidt, H., F. Jördens, G. Schmidmayer, WO 00/36034, 11.12.1998 134 M. Brand, Z. Naturforsch. 54 b, (1999) 155–164 135 S. Savard, L.P. Blanchard, Polym. Compos. 5, (1994) 242 136 L. Delattre, C. Dupuy, F. Babonneau, J. Sol-Gel Science and Technology, 2, (1994) 185–188

VIN Sepeur engl 05 AM.indd 160

21.04.2008 14:26:21 Uhr

Literature

161

137 S. Langenfeld, Diplomarbeit: “Sol-Gel-Synthesen von anorganisch-organischen Kompoist-Materialien mit TiO2 als hochbrechende Phase”, Institut für Neue Materialien gem. GmbH, Saarbücken (1994) 138 S. Brück, Diplomarbeit: “Fluormodifizierte ORMOCER-Materialien”, Institut für Neue Materialien gem. GmbH, Saarbücken (1990) 139 R.F. Harris, Polymer preprints 36, 1 (1995) 475 140 R. Nass, H. Schmidt, E. Arpac, SPIE vol. 1328 Sol-Gel Optics (1990) 258–263 141 F. Tiefensee, Dissertation: “Untersuchungen des Eigenschaftsprofils von Ocrmo­ceren hinsichtlich ihrer Anwendung in der Integrierten Optik”, Institut für Neue Materialien gem. GmbH, Saarbücken (1994) 142 E.J.A. Pope, J. D. Mackenzie, J. Non-Cryst. Solids 87 (1987) 185 143 J. Sanchez, M. Reese, A. Mc Cormick, Mat. Res. Soc. Symp. Proc. Vol. 180 (1990) 144 F. Witmore, Chem. Eng. News 26, (1984) 672 145 C.G.Swain, R.M. Esteve R.H. Jones, J. Amer. Chem. Soc. 71, (1994) 965 146 D. Oostendorp, G. Bertrand, J. Stoffer, J. Adhesion Sci. Technol. 6, (1992) 171 147 K. Piana, Promotionsarbeit: “Gelpermeationschromatographische Untersuchungen zum Hydrolyse- und Kondensationsverhalten von Organoalkoxysilanen”, Würzburg (1993) 148 H. Himmel, T. Gerber, J. Non-Cryst. Solids 119, 1 (1990) 149 A. van Blaaderen, A. Vrij, J. Colloid Inerf. Sci. 156, (1993) 1 150 J.E.Mosne, S.H. Schroeter, “Calorimetric Analysis of Photopolymerizations in Ultraviolet Light-Induced Reaktions in Polymers”, Labana, S.S. (Ed), ACS Symp. Series 25 (1976), 90 151 Produktbroschüre “Photoinitiators for UV-Curing” und Datenblatt Darocure 1173, Fa. Ciba Speciality Chemicals Inc. 152 Produktkatalog “Photoinitiators for UV-Curing” Ciba Speciality Chemicals Inc. 153 H. Kloosterboer, Aspects of Analysis, Paper 9, 2 154 D. Braun, I. Alig, M. Junkler, Angew. Makromol. Chem. 250 (1997) 105 –117 155 V.V. Krongauz, C.P. Chawla, Proc. Radtech Europe`99, Berlin, November 1999, 435– 445 156 A. Priola, F. Renzi, J. of Material Science 20 (1985) 2889–2902 157 P.G. Garratt, “Strahlenhärtung”, Vincentz Verlag (1996) 158 E. Gruber, “Polymerchemie”, Dr. Dietrich Steinkopff Verlag Darmstadt (1980) 159 K.K. Dietliker, “Photoinitiator for Free Radical and Cationic Polymerisation” in Chemistry & Technology of UV-& EB Formulation for Coatings, Inks and Paints”, Vol 3, Verlag SITA Technology (1991) 160 R. Kirchmayr, Farbe + Lack, 86 (3), (1980) 224 161 H.G.O. Becker, “Einführung in die Photochemie”, Deutscher Verlag der Wissenschaften, Berlin, 3. Aufl (1991) 162 E. Gruber in: Polymerchemie, “Eine Einführung in die Chemie und physikalische Chemie der Makromoleküle”, Dr. Dietrich Steinkopff Verlag GmbH Co. KG., Darmstadt (1980) 163 P.K.T. Olding, “Photoinitiators for Free Radical and Cationic Polymerisation” in Chemistry & Technology of UV-& EB Formulation for Coatings, Inks & Paints, Vol.3, Verlag SITA Technology (1991) 164 H. Baumann, H. J. Timpe, Z. Chem., 23. Jg. (1983) Heft 6, 197

VIN Sepeur engl 05 AM.indd 161

21.04.2008 14:26:21 Uhr

162 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191

Literature

P. Pappas, J. Radiation Curing, 14, (1987) 6 R.S. Davidson, J.W. Goodin, European polymer Journal 18 (1982) 597 Produktsortiment “(Meth-)Acrylat-Monomere” Fa. Röhm M. Zahnhausen, Diplomarbeit: “Untersuchungen zur Härtung von Ormocer Systemen durch Photopolymerisation mit Hilfe von Photo-DSC und magnetischer Kernspinresonanz-Spektroskopie”, Institut für Neue Materialien gem. GmbH, Saarbücken (1995) L. Delattre, C. Dupuy, F. Babonneau, J. of Sol-Gel Science and Technology 2 (1994) 185–188 N. Nishiyama, T. Asakura, K. Horie, Journal of Colloid and Interface Science, Vol. 124, No. 1, (1988) 14 L.N. Lewis, J. Appl. Polym. Sci. 42, (1991) 1551 General Electrics, Patentanmeldung US 4478876 (23.10.1984) L.N. Lewis, Chem. Mater., Vol. 7, No. 7 (1995) 1369 M.G. Tilley, Proc. RadTech International North America Conference (1992), Boston, Maßachusetts, I, 48 C. Vu, A. Eranian, C. Faurent, Proc. RadTech Europe Conference, Berlin, (1999) 523–529 N. Gupta, T.J.M. Sinha, I.K. Varma, Indian Journal of Chemical Technology Vol. 4 (1997) 130–134 C. Tronche, R. Jaria, C. P. Chawla, Proc. RadTech Europe Conference, 1999, Berlin, 719–724 H. Swofford Patentanmeldung US 4822828 (18. 4.1989) K. Rose, Mat. Res. Soc. Symp. Proc. Vol. 271 (1992), 731 General Electrics, Patentanmeldung US 4486504 (4.12.1984) G. Melford G., G. Gillette, Patentanmeldung US 5242719 (7. 9.1993) H. Schmidt, in: “Ultrastructure processing of Advanced Materials”, Hrsg.: D. R. Uhlmann und D. R. Ulrich. John Wiley and Sons, New York (1992) 409 C. Becker, M. Zahnhausen, H. Krug, H. Schmidt, in: “Ceramic Transactions Volume 55: Sol-Gel Science and Technology”. Hrsg.: E. Pope, S. Sakka und L. Klein, American Ceramic Society (1995) 299 R. Nass, E. Arpac, H. Schmidt, “Monolithic Gel Preparation from Chemically Modified Zirconium Alkoxides”, Proceedings Third international Conference on Ceramic Powder Processing Science, San Diego (1990) H. Schmidt, H. Krug und P. Oliveira, “Sol-gel nanocomposites for optical materials”, In: Applied Organometallic Chemistry, Bd. 5 “Chemical Routes” Hrsg.: R. Laine K. Greiwe, W. Glaubitt, S. Amberg-Schwab, K. Piana, Mat. Res. Soc. Symp. Proc. vol 271 (1992) 725 H. Schmidt, M. Mennig et al. Patentanmeldung DE 4130550 (13. 9.1991) B. Sepeur-Zeitz, Promotionsarbeit: “Mikrostrukturierung organisch-anorganischer Kompositmaterialien über Prägeverfahren”, Institut für Neue Materialien gem. GmbH, Saarbücken (1999) R. Kasemann, H. Schmidt, S. Brück, Bol. Soc. Esp. Ceram. Vid. 31-6 , Vol. 7, (1992) 75 R. Kasemann, S. Brück, H. Schmidt, Referate zur DGG-Jahrestagung 1992, 29 R. Kasemann, H. Schmidt, “Coatings for Mechanical and Chemical Protection Based on Organic-Inorganic Sol-Gel Nanocomposites”, In: Proceedings of the First European

VIN Sepeur engl 05 AM.indd 162

21.04.2008 14:26:21 Uhr

Literature

192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207

208 209 210 211

163

Workshop on Hybrid Organic-Inorganic Materials (Synthesis, Properties, Applications), Nov. 8.–10., 1993, Bierville (Paris)/France, 171–180 E. Arpac, H. Krug et.al. Patentanmeldung DE 19719948 (13. 5.1997) DIN 53151 ASTM D 3359-78 H. Schmidt, Chemistry of Material Preparation by the Sol-Gel Process, J. Non-Cryst. Solids 100, 1988, 51-64 C.J. Brinker, G. Scherer, Sol-Gel-Science: The Physics and Chemistry of Sol-Gel Processing, Academic Press Inc., Boston 1990 J. Wen, G.L: Wilkes, Organic/Inorganic Hybrid Networks Materials by the Sol Gel Approach, Chem. Mater. 8 (1996), 1667-1681 K.H: Haas, S. Amberg-Schwab, K. Rose, Functionalized Coating Materials based on Inorganic-Organic Polymers, Thin Solid Films 351, (1999) 198–203 Patentanmeldung NANO-X GmbH WO 02/50191 A2, “Lösungsmittelarme Sol-Gel Systeme” S. Sepeur, N. Kunze, S. Goedicke: European Coatings Conference (ECC) ”Modern Coatings for Plastics Substrates”,”Ultra Scratch Resistant Coating Systems”, 24. und 25. November 2003, Berlin NANO-X GmbH, Patentanmeldung Quelle: www.asicoverbuildings.com/images/mfg_hotdipped.jpg Abschlußbericht zum AIF-Vorhaben 13474 N “Neuartiger Korrosionsschutz durch Self-Assembled Monolayers aus derivatisierten leitfähigen Polymeren” Stand Januar 2005 Quelle: SAM – Self Assembling Molecules erobern den Rädermarkt, www.chemetall.de Protecting metals with silane coupling agents, van Ooij, W J; Child, T , Chemtech (USA). Vol. 28, no. 2, pp. 26–35. Feb. 1998 Quelle: K. Steinhoff, http://idw-online.de/pages/de/news106226 S. Goedicke (NANO-X GmbH), U. Paar (Volkswagen AG, Kassel), SchauplatzNano Pressekonferenz, Beiersdorff, Hotel Maritim Frankfurt 23.2.2005, Vortrag “Entwicklung einer multifunktionalen Beschichtung für die Kalt- und Warmumformung von höchstfesten Vergütungsstählen” S. Sepeur, Multifunktionale Beschichtung für die Kalt- und Warmumformung von höchstfesten Vergütungsstählen, Stahl und Eisen 5/2005, S. 68f. S. Sepeur, S. Goedicke, European Coatings Conference (ECC), 9.–10. Juni 2005, Berlin, “Smart Coatings IV”, Vortrag ”Nano-Coatings in Hot-Forming Processes on Steel Parts” S. Goedicke, Industrieanzeiger 2005, Ausgabe 25, S. 35, “Nano-Schicht verhindert, daß es Zunder gibt” S. Sepeur, N. Laryea, C. Thurn, A. Muth, “Crosslinking à la Carte”, European Coatings Journal 10 (2007), S. 48

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List of abbreviations

List of abbreviations ∆Hm

specific polymerization enthalpy ∆Hm, max maximal specific polymerization enthalpy ∆Hn molar polymerizaton enthalpy ∆Hn, max maximal molar polymerization enthalpy 1,6-HDDMA 1,6-hexandioldimethacrylat AlO(OH) boehmit ATR attenuated total reflectance BP bisphenol compound BPA 2,2-bis(4-hydroxyphenyl)propan, bisphenol A bis(2-hydroxyphenyl)-methan BPF2 BPS bis(4-hydroxyphenyl)-sulfon, bisphenol S CC-Effect catalytic clean effect CNT carbon nanotubes CR39 poly-(bisallylcarbonatsiethylenglykol) CVD chemical vapor deposition “Darocure”1173 2-hydroxy-2-methyl-1-phenylpropan-1-on, Ciba DDDMA 1,12-dodecandioldimethacrylat DEGDEE diethylenglykoldiethylether DLS dynamic light scattering DIAMO 3-(2-aminoethylamino)propyltrimethoxysilane DMDEOS dimethyldiethoxysilane DTA differential thermo analysis EDX energy dispersive X-ray analysis ESCA electron spectroscopy for chemical analysis FTS 1H,1H,2H,2H,-perfluoroctyl triethoxysilane FTIR Fourier-transformations-IRspectroscopy GPTES 3-glycidoxypropyl triethoxysilane GPTMS 3-glycidoxypropyl trimethoxy­ silane GT crosscut Stefan Sepeur: Nanotechnology © Copyright 2008 by Vincentz Network, Hannover, Germany

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HPDEC Haze

high power decoupling transmission loss by scattered light HDDA 1,6-hexandioldimethacylat INM Institut für Neue Materialien gem. GmbH IPE isopropoxyethanol IR infrared “Irgacure” 184 1-hydroxycyclohexylphenylketon, Ciba “Irgacure” 500 benzophenon/1-hydroxycyclohexyl-phenylketon mixture, Ciba K inorganic degree of condensations MWNT multi wall carbon nanotubes MI 1-methylimidazol mol% percent mole MPTS 3-methacryloxypropyl trimethoxysilane MTEOS methyltriethoxysilane MTKS MTEOS/TEOS/silica sol NIR near infrared NMR nuclear magnetic resonance ORMOSIL organically modified silanes ORMOCER organically modified ceramics PC polycarbonate PCS photon correlation spectroscopy Photo-DSC photo differential scanning calorimetry PMMA polymethylmetacrylat SEM scanning electron microscopy RT room temperature SAXS small angle X-ray scattering st stoichiometric TEM transmission electron microscopy TEOS tetraethoxysilane Tg glass transition temperature Tmax peak temperature under UV radiator TMPTA trimethylolpropantriacrylat TMS tetramethylsilane TT tape test UV ultraviolet VIS visible wt.% percent weight

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Authors

165

Authors Dr. Stefan Sepeur studied from 1989 to 1994 at the University of the Saarland, Germany. He graduated in 2001 on the development of coating materials based on the sol-gel-process. As head of department for “Materials and Process Development” he was in charge for numerous R&D projects and also manger of the application center of the Institute for New Materials (INM), Saarland. In August 1999, he joined forces with engineer Reimund Krechan to establish NANO-X GmbH. Besides his duties as managing director Dr. Sepeur has earned his place as one of the nation’s recognized specialists in the field of nanotechnology and occupies an honorary post as scientific advisor to INM. Dr. Frank Groß studied chemistry at Saarland University, gaining his diploma in low-friction sol-gel coatings for polymers and his doctorate in the field of special glass for optical waveguide amplifier at the Institute for New Materials (INM) in Saarbrücken, Germany. Between 1998 and 1999 he was in charge of a R&D group at the department of Dr. Sepeur at INM. Since 2000 he has been at NANO-X GmbH where he is department leader and responsible for developing easy to clean, catalytic and self-cleaning coatings for industrial application. Dr. Stefan Goedicke studied chemistry at the Saarland University from 1989 to 1995 and completed a semester abroad at the University of Surrey in Guildford, England. After his graduation he did his doctorate at INM (Institute for New Materials) in Saarbrücken, Germany. In industrial sponsored projects he was engaged with the development of inorganic binders based on sol-gel- und chemical nanotechnology for fire protection, high temperature resistant coatings, heat insulation and modification of dental fillers. Since 2001 he is in charge of a R&D department at NANO-X GmbH, which deals with the development of coatings for corrosion protection and high-temperature corrosion protection, as well as special applications. Dr. Nora Laryea studied from 1990 to 1995 at the technical Martin Luther University/Merseburg in Halle-Wittenberg, Germany. She received her doctorate during her course as scientist at the Institute for New Materials (INM) in Saarbrücken, Germany, in 2001. Her dissertation concerned with the development of flexible hard coating based on inorganic-organic nano-composites. Between 1998 and 2000 she was group leader in INM for the development of radiation curing nano-coatings. Since 2000 she is a shareholder of NANO-X and department leader for hard coatings, textile impregnation and binders and responsible for the care of quality assurance.

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166

Index

Index Symbole 1-methylimidazol 92 3-glycidyloxypropyl trimethoxysilane 93 3-methacryloxypropyl trimethoxysilane 112

compatibilization 113 composites 28 condensation 22 condensation speed 29 contact angle 37 corrosion protection 143

A

D

abrasion resistance 101 acidic catalysis 92 acidic hydrolysis 27 aerogel 25 Aerosil 52 Aerosil method 54 agglomeration 59, 114 alkaline catalysis 92 alkaline hydrolysis 27 aluminum alkoxide 34 aluminum alkoxides 33 anatase 69, 71 anti-fingerprint-coatings 138 anti-fog effect 46

degree of condensation 108 degree of conversion 124 degree of hydrolysis 108 diesel particulate filter 77 DLS 64 dynamic light scattering 64

B

flame hydrolysis 54 FTIR 123

BET 63 bisphenol A 93 boehmite 99 bottom-up strategy 13

C catalytic clean-effect 74 cathodic corrosion protection 148 chemical nanotechnology 14 chemical precipitation 55 chitosan 87 Stefan Sepeur: Nanotechnology © Copyright 2008 by Vincentz Network, Hannover, Germany

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E easy to clean effect 41 EDX 61 electrostatic stabilization 58 electrosteric stabilization 59

F

G gel 24 glass chemistry 21 GPTS 91

H haze 98 hot stamping 149 hydrolysis 22 hydrolysis speed 28 hydrophilic coatings 50 hydrophobic 39 hydrophobicity 39

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Index

I inductive effects 29 inorganic crosslinking 140 inverse lotus effect 49 IR spectroscopy 96 isoelectric point 59

K Karl-Fischer-titration 118

L lotus effect 36 lotus plant 43 lyogel 24

M metal alkoxides 22, 31 microemulsion method 56 MPTS 112

N nano reactors 56 nanocomposite 91 nanomaterials 11 nanometer 11 nanoparticle, production 52 nanoparticles 51 nanostructuring 15, 48 nanotubes 81 network formers 89 network modifier 28, 29 nitrogen adsorption 63 NMR-spectroscopy 108

O organosilane 19 ORMOCER 90 ORMOSIL 90 oxirane ring 92

P PCS 64 phase separation 136

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pH-level 116 photo catalysis 71, 72 photo initiators 130 photo oxidation 72 photocatalysis 70 photo-DSC 123 photon correlation spectroscopy 64, 137 precipitation emulsion method 135 press hardening 149

R refraction index 51 refraction value 35 resin 137 rutile 69

S SAM 145 SAXS 65 scaling 149 scattered light loss 98 scratch resistance 101 scratch resistant coating 102 self assembling monolayer 145 self-cleaning effect 72, 74 silane 19 silanization 20, 59 silica sols 66 silicone bridges 60 silicone chemistry 21 silicones 30 silixanes 139 silver 85 sintered metal filter 78 small angle X-ray scattering 65 sol-gel-process 22, 56 steric effect 29 steric stabilization 58, 114 Stöber-process 25 stoichiometry of hydrolysis 103 super-hydrophilic 39 super-hydrophobic 39 surface atoms 17 surface effects 36

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Index

surface energy 36 surface modification 57

T Taber-Abraser 98 TEM 60, 118 temperature profile 115 TEOS 21 textile impregnation 45 thermal corrosion protection 77 thixotropy 55 titanium dioxide 69 top-down method 52 top-down strategy 13 translucent 114 transmission electron microscopy 60, 118

U UV curing 112 UV protection 70

W wetting 37 windshield 47

X xerogel 24 X-ray diffraction 62

Y Young`s equation 37

Z zeta potential 59 zirconium alkoxides 33

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