Smart Polymer Nanocomposites: Biomedical and Environmental Applications 012819961X, 9780128199619

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SMART POLYMER NANOCOMPOSITES

Woodhead Publishing Series in Composites Science and Engineering

SMART POLYMER NANOCOMPOSITES Biomedical and Environmental Applications Edited by

SHOWKAT AHMAD BHAWANI Associate Professor, Department of Chemistry, Faculty of Resource Science and Technology, UNIMAS, Malaysia

ANISH KHAN Chemistry Department, Faculty of Science, Center of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah, Saudi Arabia

MOHAMMAD JAWAID Biocomposite Technology Laboratory, Institute of Tropical Forestry and Forest Products, Universiti Putra Malaysia, Serdang, Selangor, Malaysia

An imprint of Elsevier

Woodhead Publishing is an imprint of Elsevier The Officers’ Mess Business Centre, Royston Road, Duxford, CB22 4QH, United Kingdom 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States The Boulevard, Langford Lane, Kidlington, OX5 1GB, United Kingdom © 2021 Elsevier Ltd. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library ISBN: 978-0-12-819961-9 (print) ISBN: 978-0-12-820435-1 (online) For information on all Woodhead publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Matthew Deans Acquisitions Editor: Gwen Jones Editorial Project Manager: Charlotte Rowley Production Project Manager: Surya Narayanan Jayachandran Cover Designer: Christian J. Bilbow Typeset by SPi Global, India

Contributors M.K. Abdul Rahim University of Technology and Applied Sciences, Muscat, Oman

Sadaf Afrin Institute of Architecture and Civil Engineering, South Ural State University, Chelyabinsk, Russia; MoRe € € Research Ornsk€ oldsvik AB, Ornsk€ oldsvik, Sweden

Nayeem Ahmed Department of Chemistry, University of Kashmir, Srinagar, India

Hanan AlBuflasa Department of Physics, College of Science, University of Bahrain, Sakhir, Bahrain

Basma Al-Najar Department of Physics, College of Science, University of Bahrain, Sakhir, Bahrain

Khalid M. Alotaibi Department of Chemistry, College of Science, King Saud University, Riyadh, Kingdom of Saudi Arabia

Mohd Razip Asaruddin Faculty of Resource Science and Technology, Universiti Malaysia Sarawak (UNIMAS), Kota Samarahan, Sarawak, Malaysia

Yasser Azim Department of Applied Chemistry, Z.H. College of Engineering & Technology, Aligarh Muslim University, Aligarh, India

Krithika Balakrishnan Laboratory for Bioremediation Research, Unit Operations Lab, Department of Biotechnology, Kumaraguru College of Technology, Coimbatore, Tamil Nadu, India

Fawzi Banat Department of Chemical Engineering, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates

A.H. Bhat University of Technology and Applied Sciences, Muscat, Oman

Mushtaq Bhat (Ahmad) Islamic University of Science and Technology, Awantipora, India

Showkat Ahmad Bhawani Faculty of Resource Science and Technology, Universiti Malaysia Sarawak (UNIMAS), Kota Samarahan, Sarawak, Malaysia

Debarupa Dutta Chakraborty Department of Pharmaceutical Analysis, Himalayan Pharmacy Institute, Majitar, Sikkim, India

Prithviraj Chakraborty Department of Pharmaceutics, Himalayan Pharmacy Institute, Majitar, Sikkim, India

B.T. Darsini Laboratory for Bioremediation Research, Unit Operations Lab, Department of Biotechnology, Kumaraguru College of Technology, Coimbatore, Tamil Nadu, India

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Swapnil Dharaskar Nano-Research Group, Department of Chemical Engineering, School of Technology, Pandit Deendayal Petroleum University, Gandhinagar, Gujarat, India

Saba Farooq Faculty of Resource Science and Technology, Universiti Malaysia Sarawak, Kota Samarahan, Sarawak, Malaysia

Sana Farooq Department of Biotechnology, Lahore College for Women University, Lahore, Pakistan

Chin Suk Fun Faculty of Resource Science and Technology, Universiti Malaysia Sarawak, Kota Samarahan, Sarawak, Malaysia

U. Gazal Raja Bahadur Venkata Rama Reddy Women’s College, Hyderabad, India

Bharath Govindan Department of Chemical Engineering, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates

Eva Gupta Department of Electrical Engineering, Amity University, Noida, Uttar Pradesh, India

Abdul Hai Department of Chemical Engineering, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates

Haryanto Chemical Engineering Department, Universitas Muhammadiyah Purwokerto, Purwokerto, Indonesia

Awang Ahmad Sallehin Awang Husaini Faculty of Resource Science and Technology, Universiti Malaysia Sarawak, Kota Samarahan, Sarawak, Malaysia

Mohamad Nasir Mohamad Ibrahim School of Chemical Sciences, Universiti Sains Malaysia, Gelugor, George Town, Pinang, Malaysia

Nand Jee Kanu Department of Mechanical Engineering, S. V. National Institute of Technology, Surat, India

Zoheb Karim Institute of Architecture and Civil Engineering, South Ural State University, Chelyabinsk, Russia

Imran Khan Sultan Qaboos University, Muscat, Oman

Mohammad Mansoob Khan Chemical Sciences, Faculty of Science, Universiti Brunei Darussalam, Gadong, Brunei Darussalam

Abdul Moheman Department of Chemistry, Gandhi Faiz-e-Aam College (Affiliated to M. J. P. Rohilkhand University), Shahjahanpur, India

Mu. Naushad Department of Chemistry, College of Science, King Saud University, Riyadh, Saudi Arabia; Yonsei Frontier Lab, Yonsei University, Seoul, South Korea

Zainab Ngaini Faculty of Resource Science and Technology, Universiti Malaysia Sarawak, Kota Samarahan, Sarawak, Malaysia

Mehvish Nisar Faculty of Resource Science and Technology, Universiti Malaysia Sarawak (UNIMAS), Kota Samarahan, Sarawak, Malaysia

Contributors

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Tabassum Parveen Department of Botany, Aligarh Muslim University, Aligarh; Department of Environmental Engineering, Indian Institute of Technology, Roorkee, India

K. Rambabu Department of Chemical Engineering, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates

Mohd Rashid School of Chemical Sciences, Universiti Sains Malaysia, Gelugor, George Town, Pinang, Malaysia

Hairul Azman Roslan Faculty of Resource Science and Technology, Universiti Malaysia Sarawak, Kota Samarahan, Sarawak, Malaysia

Muhammad Taqi-uddeen Safian School of Chemical Sciences, Universiti Sains Malaysia, Gelugor, George Town, Pinang, Malaysia

Ho Wei Seng Faculty of Resource Science and Technology, Universiti Malaysia Sarawak, Kota Samarahan, Sarawak, Malaysia

Jatin Sethi KTH Royal Institute of Technology, Stockholm, Sweden

Aabid Shalla (Hussain) Islamic University of Science and Technology, Awantipora, India

Ngieng Ngui Sing Faculty of Resource Science and Technology, Universiti Malaysia Sarawak, Kota Samarahan, Sarawak, Malaysia

Gyanendra Kumar Singh Department of Mechanical Design and Manufacturing Engineering, Adama Science and Technology University, Adama, Ethiopia

N. Sivarajasekar Laboratory for Bioremediation Research, Unit Operations Lab, Department of Biotechnology, Kumaraguru College of Technology, Coimbatore, Tamil Nadu, India

Apsara Sudhakar Laboratory for Bioremediation Research, Unit Operations Lab, Department of Biotechnology, Kumaraguru College of Technology, Coimbatore, Tamil Nadu, India

Abu Tariq Department of Chemistry, Aligarh Muslim University, Aligarh, Uttar Pradesh, India

Khalid Umar School of Chemical Sciences, Universiti Sains Malaysia, Gelugor, George Town, Pinang, Malaysia

Umesh Kumar Vates Department of Mechanical Engineering, Amity University, Noida, Uttar Pradesh, India

Micky Vincent Faculty of Resource Science and Technology, Universiti Malaysia Sarawak, Kota Samarahan, Sarawak, Malaysia

Asim Ali Yaqoob School of Chemical Sciences, Universiti Sains Malaysia, Gelugor, George Town, Pinang, Malaysia

Preface Smart polymers are capable of undergoing rapid change, reversible phase transition from a hydrophilic to a hydrophobic microstructure when triggered by a small change in their environment such as temperature, pH or ionic strength, light, magnetic or electric field, etc. The living systems respond to external stimuli and adapt themselves to changing conditions. In this context, polymer scientists have been trying to mimic this behavior for the last two decades to make smart polymers. Smart polymers have shown promising applications in various fields such as delivery systems for drugs, tissue engineering scaffolds, cell culture sports, bioseparation, and sensors or actuator systems. The present book is a collection of valuable reference materials for researchers working in the fields of materials science, biomaterials, regenerative medicines, drug delivery, polymer science/chemistry, chemical engineering, mechanical engineering and in the polymer industry. This book will be useful for scientists working on bioseparation and bioprocessing. This will be very helpful for the students in the development of new polymers as well as graduates in polymer technology, environmental science, and biotechnology. This book covers topics such as Introduction, Processing and Properties, Manufacturing and design of smart polymer composites, Shape memory polymer composites, Smart polymer hydrogels, Smart biopolymers, Enzyme-responsive polymer composites and its applications, Biomedical applications of smart polymer composites, Smart polymer composites for tissue engineering, Nanomedicine, bioseparation, drug delivery, environmental applications, membranes for wastewater treatments, textile and plastics, wood protection, protection of corrosion, and antifouling application. We are highly thankful to all the authors who contributed book chapters and provided their valuable ideas and knowledge on Smart Polymer Nanocomposites for Biomedical and Environmental Applications in this edited book. We have made an attempt to gather all this information from recognized researchers from Malaysia, India, Morocco, Bangladesh, Italy, and Egypt in the areas of smart polymer nanocomposites and finally

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complete this venture in a fruitful way. We greatly appreciate the authors’ commitment to their support to compile our ideas in reality. We are highly thankful to the Elsevier team for their generous cooperation at every stage of the book’s production. Showkat Ahmad Bhawani Anish Khan Mohammad Jawaid

CHAPTER ONE

Introduction of smart polymer nanocomposites Asim Ali Yaqooba, Muhammad Taqi-uddeen Safiana, Mohd Rashida, Tabassum Parveenb,c, Khalid Umara, and Mohamad Nasir Mohamad Ibrahima a

School of Chemical Sciences, Universiti Sains Malaysia, Gelugor, George Town, Pinang, Malaysia Department of Botany, Aligarh Muslim University, Aligarh, India Department of Environmental Engineering, Indian Institute of Technology, Roorkee, India

b c

1.1 Introduction Smart materials are usually projected as those materials that have the ability to change the performance or properties by changing the environmental stimulus. Therefore, these types of materials are usually sensitive to their environmental parameters such as pH, light intensity, temperature, magnetic field, pressure, electrical field, etc. The exterior stimulus of these materials shows several responses such as color variation, altering conductivity, cumulative dielectric constant, and better self-healing quality [1]. Smart polymer nanocomposites attract a great deal of attention in the modern era due to their high-performance properties in several types of applications. However, the polymer is a large molecular weight compound, which is composed of repeated monomeric units. It has become a great material of concern to researchers for several centuries [2]. The most commonly used natural polymers are rubber and wood. These are broadly used in natural polymeric materials but their consistent property and essential structure limits their extensive applications in up-to-date industries. However, scientists began to use several types of modification methods to change the natural polymers into more valuable materials. For example, the nitrocellulose synthesis approach by the chemical reaction of cellulose and nitric acid formed vulcanized rubber by the thermal approach under sulfur atmosphere [3]. These kinds of improved natural polymers are broadly used commercially even in the present time. However, improved natural polymers are not sufficient as compared with modern demands. Therefore, the materials science has bought a simulated revolution through the initiation of synthetic-based polymers. In polymer industries the functional typed polymers and smart Smart Polymer Nanocomposites https://doi.org/10.1016/B978-0-12-819961-9.00007-4

© 2021 Elsevier Ltd. All rights reserved.

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polymer have been widely studied in the 20th century [4, 5]. The idea of smart polymer composites offers several innovative applications beyond the conventional polymers. The most frequently used smart polymers are electroactive polymers (EAPs), remendable polymers, and ferroelectric polymers. The EAPs are a collection of smart polymeric materials, the size, shape, and morphology of which are modified under the effect of an electric field. Remendable polymers are also called healable polymers as they are a type of smart polymers that can recapture their damage through external stimulus such as heating stimuli or self-healing [6]. Similarly, ferroelectric polymers sustain an everlasting electric polarization that can be overturned or transferred by an electric field. Polyvinylidene fluorides (PVDFs) are extensively used in electromechanical and acoustic transducers due to their properties such as intrinsic piezoelectric feedback and thermal sensing [7]. Overall, their benefits originate from composite materials and from the significant progress made of smart polymeric materials. However, another important aspect is nanotechnology which is widely familiar to be most capable zones for scientific development. It generally refers to the operating matter at the molecular level and utilizing the structures and materials with nanosize measurement; mostly the range is from 1 to 100 nm. Particles in the nanosize range demonstrate exclusive physiochemical properties like great surface area to volume ratios or higher interfacial reactivity. The high performance of nanorange particles has been studied to show precise interface with pollutants in gases, soil, and water. The high-performance properties of nanoparticles offer a hope for stimulating innovative and enhanced environment-based technology. The smart polymer nanocomposites are included as elastomers, thermosets, and thermoplastics that have been strengthened with nano measurements of nanosized particles with higher aspect ratios [8]. Furthermore, polymeric nanocomposites can be categorized into three main forms such as intercalated, flocculated, and exfoliated nanocomposites. In the case of intercalated nanocomposites, polymer chains are introduced into covered structures like clay. Clay presents itself in a crystallographic steady form, with some nanometer replication distance, unrelatedly of polymeric ratio of coated structure. However, the flocculation of introduced and weighted layers to roughly extent is carried out due to the edge-edge hydroxylated interactions in the clay layers. Similarly, in exfoliated nanocomposites parting of the distinct layers in the polymeric medium present in another type by regular reserves that rely on the stacking of the coated material, e.g., clay. Polymeric nanocomposite materials that carry higher

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storage modulus, improved tensile and high flexural activities, thermal distortion, reduction in gas permeability, and exclusive features such as biodegradability and self-extinguishing characteristics are studied [9]. Additionally, the living classifications respond to logically fluctuating ecological conditions, adjusting their functionality and structure, to suit these fluctuations through utilizing the composite sensing mechanisms, regulating and actuating functions, and response controller systems. Nature can be a significant example for developing and formulating a novel material and their use in several types of applications. However, the general challenge for researchers is to produce a potential material with active and remarkable properties, mimicking the dynamic environment at the nanolevel present in nature. Polymeric materials that hold the capacity to reply toward exterior stimuli are denoted as stimuli-responsive polymers or smart polymers. Smart polymers experience a great reversible change, either chemical or physical, in their properties as a significance of minor ecological differences. They can reply to a single, dual, or multiple stimulus such as the electric field, temperature, magnetic field, pH, light intensity, living molecules, etc. This response encourages the macroscopic feedbacks in the material, e.g., collapse/swelling or solution/gel transitions that potentially depend on the physiochemical state of response chains [10]. Solubilized and linear smart larger molecules will permit movement from monophasic stage to biphasic stage nearby the transitional environments giving rise to adjustable sol-gel hydrogels. The smart cross-linked systems experience the chain rephrasing at transitional situations, where the system permits from a collapsed to a prolonged estate. The variation in smart surfaces changes the hydrophilicity of the provided stimulus and responsive interface [11]. All these variations can be used to strategize these polymers for several applications. The slightly aggressive injectable structures which are pulsatile to drug delivery approach or novel substrates for cell tissue culture or cell engineering are considered as examples of variations [12]. Likewise, the polymers are easily be functionalized through earlier polymerization or later polymerization approaches and integrated from functional fragments to the assembly, such as living receptors. Therefore, there are extensive varieties of potentials in polymeric-based chemical structures, polymeric architectures, and modified polymers to progress an unlimited number of applications for these smart materials [13]. However, earlier smart polymer-based materials have been used extensively in biological and chemical sciences in various ways. Moreover, the smart polymer-based materials involved an extensive range of diverse compounds with exclusive

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possibility for living applications, and meanwhile the attention in producing and operating these complexes is growing day by day. Smart polymeric material responds to minor changes in their atmosphere with changes in their physiochemical properties. In short, the smart polymer is considered as reversibly soluble-in-soluble (SIS) in an aqueous medium or crossconnected in the hydrogel form [14]. Certainly, hydrogel is a network of hydrophilic-based polymers and present in two forms such as physical and chemical hydrogels. Physical hydrogels are detained together with noncovalent services, while chemical hydrogel is achieved through chemical cross connecting, but both types of hydrogels are physically similar. Furthermore, physical hydrogels contain hydrophobic and hydrophilic domains. Chemical-based hydrogels contain “clusters” or areas of high cross-connecting density in low swelling structures, while in high swelling it contains low cross-linking density polymer network [15, 16]. Both soluble-in-soluble and hydrogel polymers have been exposed and respond to a small variation of stimuli like change in light, temperature, electric field, pH, ionic strength, and magnetic field. Some most common stimuliresponsive smart polymer materials are presented in Table 1.1. In this chapter, the main objective is to elaborate the importance of smart polymers and their composite materials at the nano scale. Smart polymer classification along with the most familiar synthesis methods and some most common applications are briefly summarized in this chapter.

1.2 Classification of smart polymer nanocomposites The polymer that holds an ability to facilitate the external stimuli is referred as stimuli-responsive polymers or as smart polymers. Smart polymers can facilitate toward the stimuli in numerous ways by changing the conductivity, shape, color, wettability, and light-conducting facilities. The ratio of response of smart polymers can be controlled and regulated through the intensity of functional stimuli. Scientists have industrialized several responsive polymers and used in many stimuli such as light intensity, pH, temperature, electric field, humidity, and magnetic field. The change and control of physiochemical properties of smart polymers are highly appropriated for several domestic and commercial applications. Smart polymer composites can be generally classified into three groups: (i) single stimulus, (ii) dual stimulus, and (iii) multistimuli-responsive polymers and are shown in Fig. 1.1 with their subclassifications [38, 39].

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Table 1.1 List of different type of stimuli with responsive smart polymer materials. Smart polymer material Type of stimuli Reference

Ultrasound Polyacrylamide-triphenylmethane leuco derivatives Dodecyl isocyanate-modified PEG-grafted poly (HEMA) Poly(vinyl alcohol)-graft-poly-acrylamideLight and triphenylmethane leucocyanide derivatives temperature Poly(N-vinyl carbazole) composite IR radiation Carboxymethyl cellulose Ca2+ Polythiophen gel Electric potential Polyacrylamide cross-linked with UV radiation 4-(methacryloylamino) azobenzene Poly(N-acryloyl-N-propyl piperazine) pH and temperature Eudragit S-100 Ca2+ and temperature Pnipaam hydrogels containing ferromagnetic Magnetic field material pnipaam-co-acrylamide Eudragit S-100 Ca2+ and acetonitrile Poloxamers Temperature (sol-gel transition) Chitosan-glycerol phosphate-water Temperature Prolastin Temperature Hybrid hydrogels of polymer and protein Temperature domains Eudragit S-100 Organic solvent Eudragit L-100 pH Poly(L-lysine) ester pH Poly(L-lysine)-G-poly(histidine) pH Eudragit L-100 pH Chitosan pH Polysilamine pH

[17]

[18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37]

1.2.1 Single stimulus-responsive polymers The stimuli that encourage the changes in smart polymers can be further classified into subclasses such as physical, biological, and chemical stimuli. Smart polymers respond to the physical stimuli such as a magnetic field, light, electric field, and temperature due to modification of chain subtleties, that is, polymeric energy level and solvent system. While the biological stimuli refer to the definite operation of molecules, e.g., receptor recognition and enzymatic reactions, etc., the chemical stimuli moderate molecular connections

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Fig. 1.1 Classification of stimuli-responsive polymers.

between solvent and polymeric molecules or among polymeric chains to incorporate variations in the polymers. Thermo-responsive polymer systems solved the problems related to temperature where the smart polymer system feels a phase variation within a minor temperature variety. This phenomenon is due to the disturbance of intramolecular and intermolecular relations that has occurred subsequently during the development or reduction of polymeric chains. A distinctive thermo-responsive polymer solution holds an upper critical temperature (UCST), which is one stage of the smart polymer and lower stage separation can be observed. Furthermore, smart polymer solutions that suffer monophasic below a definite temperature and crack into biphasic above that temperature are usually measured to have the lower critical solution temperature (LCST) [40]. According to the group chemistry and their mechanism, many thermo-responsive polymers have been described such as poly(N-vinylalkylamides), poly(N-alkyl-substituted acrylamides), poly(N-isopropylacrylamide), poly(N-vinylcaprolactam), and lactic acid [41, 42]. Seeboth et al. [43] defined prepared chromogenic smart polymer composite systems, which is potentially delicate to temperature variations. They prepared smart polymeric gel nanocomposite-based networks in the presence of thermochromic dyes. The dyes used were cresol red or betaine (2,6-diphenyl-4-(2,4,6-triphenylpyridinio) phenolate, DTPP), and were completely dispersed into the polymeric material known as poly(vinyl alcohol)-borax-surfactant gel at a pH of 8.5. Due to of DTPP, the composite exhibited color variations slowly from colorless at ordinary

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temperature to a profound violet. In contrast, cresol red-doped polyvinyl acryl composites showed color variations from yellowish to reddish, which was noticed for a similar temperature series. The detected adjustable color variations produced through temperature differences. For instance, DTPP showed no color at a pH of 8.5 at less than room temperature, while it changes to profound violet with rising temperature. Similarly, the light stimulus provides several flexibilities such as instant application and high precision with remarkable contact wavelength controller. The light stimulus commencement from UV to infrared permits variety in many kinds of applications, which may not be accessible via other stimuli. In addition, light can be functionalized straightly on the surface of polymers to activate a response. Highly studied photo-responsive smart polymers exist such as spiropyran, azobenzene (trans/cis isomerization), fulgide, and spiroxamine derivatives [44]. An example of light-responsive smart polymer composite is explained by Chen et al. [45] in which a flexible nanocomposite of one-phase metalbased ZnS was mixed with the polydimethylsiloxane (PDMS) medium. The prepared composite holds durable, flexible, and well-suited properties by means of random substrate aspects. Similarly, in biological stimuli, several factors are involved and the most important are represented by glucose and enzyme [46]. Glucose-sensitive smart polymers are broadly studied due to them having significant applications in drug delivery like an insulin delivery. Glucose-based smart polymers are prepared through conjugating glucose oxidase (GOX) with a pH stimuli polymer [47]. GOX oxidizes glucose molecules to gluconic acid, which produces a variation in pH of the surrounding atmosphere. In pH change response, the pH polymer demonstrates a volume transition. This extreme variation in the polymeric phase is controlled through the physique’s glucose level, which disturbs the enzyme activities. Presently, there is a great deal of attention devoted to this zone to develop biodegradable, sensitive glucose-responsive polymers. Another enzyme-responsive smart polymer is the naturally occurring bacteria situated in the colon zone that secretes distinct enzymes like glycosidases and azoreductase, which are proficient in degrading several polysaccharides with dextrin, chitosan, pectin, etc. [48]. Hereafter, a characteristic enzymeresponsive polymer does not need any exterior activation for its disintegration. However, a chemical stimulus such as pH stimulus in which polymers comprise moieties that can contribute or receive protons when there is an ecological change in pH stimuli [49]. Any variation in pH that initiates ionic relations, which lead to the failure or growth of polymeric chains in solution form, is encouraged through the electrostatic revulsion of the controls that

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are produced in this development. Distinctive pH-responsive materials are composed of polybases and polyacids; the polyacids, e.g., polyacrylic acids contribute the protons and waves under elementary conditions, while polybases included poly(N,N-dimethyl aminoethyl methacrylate) which receives protons in the presence of acidic environments and increases due to Coulomb repulsion [50]. Highly studied pH-responsive polymers are albumin, polyacrylic acid, chitosan, poly(lysine) (PL), poly(ethylene imine) (PEI), and poly(N,N-diakylamino ethylmethacrylates) (PDAAEMA) [51]. Redox stimulus has also a chemical response, which occurs due to variations in oxidation state of redox-subtle groups. These stimuli can be typically understood in inorganic interaction mainly with transitional metals. Furthermore, solvent stimuli are also a responsive polymer, which are synthesized from distorted polymers as solvent, causing a swelling of the polymer resources and raises the elasticity of the bulk molecular polymeric chains. Many polymers like poly(2-dimethylaminoethyl methacrylate), poly(ethylene glycol) (PEG), and poly(butyl acrylate) have also been studied to construct a solvent smart polymer [52]. Distortion of polymeric brushes on solvent action has opened up several novel potentials in surface manufacturing ideas. For example, Chen et al. [53] studied the distortion of poly(methyl methacrylate) (PMMA) brushes with diverse solvents. The ratio of deformation of PMMA brushes can be diverse, when dried with diverse solvents. Fig. 1.2 shows the graphic diagram of an adjustable behavior of PMMA brushes when absorbed THF (tetrahydrofuran) with water and resulted in mushroom and brushes [54]. Patterned PMMA Brush

Water immersion

d

200 nm

THF immersion

d

d

d

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6

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μm

Fig. 1.2 Schematic artworks of reversible PMMA brush treated with weak and good solvents. (Reproduced from Chen JK, Hsieh CY, Huang CF, Li PM, Kuo SW, Chang FC. Using solvent immersion to fabricate variably patterned poly (methyl methacrylate) brushes on silicon surfaces. Macromolecules 2008;41(22):8729–8736, with ACS permission.)

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1.2.2 Dual stimuli-responsive polymers The dual stimuli contain two major types; one is the thermo-light responsive polymer, while the other one is thermo-pH responsive polymer. In early 1988, Kungwatchakun et al. [55] described the initial dual-responsive polymer classification, which responds to light and heat stimuli. The thermoresponsive polymers are prepared through polymerization of acrylamide monomer (N-(4-phenylazophenyl) acrylamide) with NIPAM (Nisopropylacrylamide) [56]. Photochromic azobenzene is introduced into the aqueous medium of PNIPAAM and the stage parting solution temperature is measured and observed through the light intensity. During this development, a change from 21°C to 27°C in phase departure temperature is realized after the irradiation of UV light. This adjustable variation in LCST is credited to the variation of dipole moment from 0 to 3 debye [52]. This phenomenon occurred due to trans-to-cis isomerization of azo-benzene. The early-phase transitional temperature is reobtained through contact to observable light. Several studies have shown their consideration by means of functionalized azobenzene to form a dual-responsive polymer. However, thermoresponsive and pH-responsive polymers are sensitive to both pH and temperature, which involved a great contract of consideration in the drug delivery field as both factors can change according to requirement. This change can be used to activate autonomous feedback. The useful moieties that are accomplished through creating ionic clusters by association or dissociation and protonation are introduced into the supportive chain of LCST polymer, such as tertiary amines and carboxylic acids. In addition, convinced homopolymers like poly(2-(dimethylamino) ethyl methacrylate) (PDMAEMA) shows heat- and pH-responsive behavior while PDMAEMA does not show any such type of behavior [57]. However, cloud points become shifted to advanced ideals with growing pH due to amino functionality thus representative of dual-responsive performance. The thermo-light response carried a great influence, e.g., poly(vinylidene fluoride-co-hexafluoropropylene)graphene oxide composite-based film illustrated the adjustable glass drive due to the fragmented symmetry through revolving the observable light with on/off, i.e., 54 mW/cm2 and 450 nm. In this early state, the produced film is instantaneously exposed to the significant and the stimulating force, which save it in a symmetry state previously as light radioactivity, while throughout the recitation development, the film equilibrium is unavoidably broken, which led to the glass movement [58].

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1.2.3 Multistimuli-responsive polymers The achievement of single- and dual-responsive polymers stimulated scientists to explore and progress polymeric systems that can be an answer to the three-layered stimuli. The accumulation of alternative stimulus with dualresponsive polymers can recover the accuracy of the feedback. In addition, the presence of three-layered stimuli can also improve the substituting conditions due to higher level of polymer difficulties. Some smart polymer structures are shown in Fig. 1.3, which elaborate the single, dual, and multistimuli response properties. Tang et al. [59] prepared the polymeric system, which responds to pH, light, and temperature by means of azobenzene concluded PDMAEMA polymer through atom-transfer radical polymerization (ATRP) [60]. According to the outcomes of several studies, the LCST aspects of the industrialized polymer system can be changed by varying the pH range. For example, when no LCST is observed at pH ¼ 4 due to the high polarity produced through protonation of dimethylamine functional groups then reduction in the proton absorption, i.e., growing the pH, produced deprotonation which caused a decrease in LCST to 68°C at pH 7 from pH ¼ 11 at 30°C [61]. Using irradiation of UV light, azobenzene trans/cis photoisomerization leads to higher LCST. However, it is improved under the irradiation of visible light. This procedure is exposed to be entirely reversible. There

Fig. 1.3 Stimuli-responsive polymers; single-stimulus-responsive polymers: (A) poly (ethylene glycol) mono-methyl ether-monomethacrylate, (B) azobenzene, (C) poly(Nisopropylacrylamide), dual-stimuli-responsive polymers, (D) carboxylic acid, (E) nitroxide, (F) disulfide; multistimuli-responsive polymer, (G) poly(2-(dimethylamino) ethyl methacrylate).

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are several studies which have shown the effect of azobenzene moieties situated at the end of chain of smart polymers. The outcomes of studies recommend that the volume of azobenzene is proportional to the variation in LCST in both cases, before and after light irradiation [62]. Recently, numerous other polymer-based systems such as PNIPAAM along with spirobenzopyran, hypersplit polyethyleneimine through butyramide clusters and copolymer systems produced by utilizing the NIPAM, Nhydroxymethylacrylamide (NHMA), and 2-diazo-1,2-naphthoquinone5-sulfonylmethylacrylamide (DNQ) have been explored to prepare triple smart polymer composites [63]. For example, Liu et al. [64] studied multipolymer nanocomposites formed through chemical cross-link of cellulosic nanocrystals (CNCs) by means of polyethylene glycol (PEG) and polycaprolactone (PCL). The resultant nanocomposite have shown that PEG/ PCL/CNC offered an outstanding thermo-induced effect at 37°C and the CNC introduction undoubtedly enhanced the mechanical aspects of the composite with lower molecular weights. So, this thermo-responsive nanocomposite might be industrialized into a novel smart biomaterial. Another most familiar multistimuli is light, thermo, and redox approachable polymers. Several courses of three-layered responsive systems such as light, thermo, and redox polymer systems are prepared using different redox vigorous moieties. The prepared three-layered smart polymer system using the PNIPAAM copolymers is composed of amino-functionalized azobenzene and 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (amino-TEMPO) moieties related via the amide bond of polymeric backbone [65]. The TEMPO moiety can be condensed through using ascorbic acid, which is a minor reducing agent and reoxidized through significant oxidizing agent, e.g., red prussiate. To excite azobenzene chromophore, the polymer is treated with UV light. This act further leads to an increase in the LCST. Though there is no change in LCST values unrelated to the order of functional stimuli toward the two responsive clusters, the middle LCST values are observed to be contingent on classification of stimulation. When azobenzene is inspired initially, the influence produced through azobenzene moiety which is around more than 60% stronger as compared to prior reduced copolymer [66]. This occurs due to the polarity effect of azobenzene in the hydrophobic state as compared to the effect of isomerization present inside the previously hydrophilic copolymer. However, further dual/multistimuli smart polymer systems include ecological pH, thermo-redox systems, and temperaturebased systems, etc. which are specific in action.

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1.3 Application of smart polymer composite materials This part comprises most familiar applications and the value of smart polymers in several fields according to the well-known scientific community. Most of the significant progresses were recorded in the environment and biomedical field. The use of smart polymeric composites in the progress of innovative treatments for several types of dangerous diseases or cultured medical apparatus that respond to the atmosphere such as analyte, pH, pressure, temperature, concentration, enzymes, etc. and external stimuli included magnetic radiation, light, etc. Some common applications of smart polymers are discussed here such as sensor applications, drug delivery, catalytic application, etc.

1.3.1 Sensor/biosensor and their types In the last 20 years, smart polymeric sensors have attracted specific attention of the scientific community. It is well acknowledged that the meaning of sensing behavior related to smart polymers is to offer data about the atmosphere in which the factual condition is situated. The outline of more legislative acts has increased the necessity for growth of equipment for regulating and controlling different human parameters that can become a dangerous alarm for anthropological life-like existence of contaminated vapors and toxic gases, water effluence caused through industrial wastes, or insecticides utilized in harvest fields [67]. Another zone in the requirement of integration of such resources and driving their growth is medicine. Polymer is considered as a material that can be modified to definite tasks by their suitable variation, which found excessive use in the progress of sensor devices. Modern literature analysis shows that smart polymer materials and their composites are considered as the most frequently used resources in the fabrication of sensors with several applications. However, the difference between sensors and biosensors is: a sensor is basically a self-contained combined device, which have the ability to accept an input from its environments and change it into an output indicator that can be handled and changed to a clear result, while a biosensor has the capacity to detect and quantify the biotic species. Overall, a biosensor must be accomplished of sensing a species of concentration (analyte) from a multifaceted mixture comprising a diversity of interfering class and must offer a precise outcome in a quick time. However, biosensors must be able to sense biological substance in reserve-limited sceneries and at point-of-care (POC) to enhance

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the performance of treatment in the modern world. Smart polymer-based biosensors/sensors have received considerable attention due to their capacity to change the existence of analytes into chemical or physical variation [68–70]. For example, Toma et al. [71] produced a poly(Nisopropylacrylamide)-co-methacrylic acid (pNIPAm-co-MAAc) hydrogel with indium TiO2 microheater composites on the surface plasmon resonance (SPR) sensors, which permits SPR sign modification as shown in Fig. 1.4. Microheaters utilizing the quick heat responses of pNIPAm-coMAAc material among the de-swollen and the swollen could be activated, yielding a thermo/optical constant of dn/dT ¼ 2  102 RIU K1. Moreover, the hydrogel coating can act as a 3D obligatory medium for sensor/ biosensor applications through manufacturing bio-recognition fundamentals in terms of smart polymer network. Smart polymers modified with nanorange particles to form nanocomposite have attracted a substantial consideration in current years for detecting and biosensing [71]. The quantum effects with nanorange particles showed exclusive visual properties such as optimistic emission without photo-bleaching, which prefer as ideal applicants for correspondents in sensors. In addition, conformational modification of surface-bound smart polymeric materials can interpret into visible photosensitive property variations, which can be used for detecting and biosensing; for example, a colorimetric and salt sensor through gold nanoparticles coating (Au-NPs) with a thermo-responsive pNIPAm shell. The pNIPAm smart polymer was prepared through polymerization by using methyl 2(((butylthio)carbonothioyl) thio) propanoate (MBTTC) as a chain

Fig. 1.4 Graphic illustration of a pNIPAm-co-MAAc hydrogel improved SPR sensor with fixed microheaters allowing quick signal modification. (Reproduced from Toma M, Jonas U, Mateescu A, Knoll W, Dostalek J. Active control of SPR by thermoresponsive hydrogels for biosensor applications. J Phys Chem C 2013;117(22):11705–11712, with ACS permission.)

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transfer agent (CTA), and more fixed to the surface of the Au-NP surface through the ligand exchange method [72]. When these responses were visible to different salt meditations, the pNIPAm-AuNP-modified material was capable to modify the color from red purple or blue at high temperatures, as shown schematically in Fig. 1.5. The Au-NP accumulation encouraged electronic connection of SPR important to an observable color change.

1.3.2 Wastewater treatment Smart polymers and their composites play a vital role in wastewater treatment. For example, polybenzoxazines carried significant value due to the presence of repeat units in the chemical structure of polybenzoxazines, which has tertiary amines and phenolic hydroxyl that are appropriate for the purpose of metal chelating. Taskin et al. [73] prepared benzoxazine monomer (B-ala) by using allylamine, paraformaldehyde, and bisphenol A, as a precursor agent. The potential benzoxazine can be modified to get polybenzoxazines as sorbent substance as shown in Fig. 1.6. However, allyl having bisbenzoxazine was particularly chosen as bis-functional monomeric units to provide further cross-linked positions for network development. Also, the absorbent structure was gained through benzoxazine polymerization in DMSO solvent. Furthermore, polybenzoxazines come from B-ala can cross-link with mercuric salts due to the presence of several structural properties. The mercury salts are specifically more essential due to that the mercury toxic connected composite is high. Mercury can cause harmful effects on the brain, kidneys, peripheral nervous system, and central nervous system. As reported by Taskin et al. [73] polybenzoxazines originates from B-ala operations; specific area (45 m2/g) was observed to eliminate mercury (II) from water. The residue analysis report has shown that the sorption of mercury salt reached to 98%, which is considered more as compared with other metallic ions. However, polybenzoxazine nanocomposites were also used for the treatment of water. Si et al. [74] used aniline-based benzoxazine monomers and BA-a (bisphenol A) as initial monomers to make F3O4carbon nanofibers (Fe/CNFs), as shown in Fig. 1.7. In a distinctive experiment, the nanocomposite contains BA-a (bisphenol A) and polyvinyl butyral (PVB), and also ferric acetate (Fe(acac)3) also showed responsive behavior toward specific conditions. Subsequently, the in situ BA-a polymerization was achieved, and it cured with polyvinyl butyral to make polybenzoxazine nanofiber nanocomposites. Lastly, the obtained

N

aC

⬚C 45

O

OH O

O O

O

l(

0.

Δ@

1M

)

Red

OH

NaCl (0.2M or

Au(III) O S

S n

Red

S HN

above)@RT

O

O

Blue-purple

N

aC

l(

Red

0.

⬚C

1M

45

)@

Δ@

RT

Red

Fig. 1.5 Graphic illustration of pNIPAm-AuNPs modification and their heat-responsive behavior in an aqueous medium. (Reproduced from Maji S, Cesur B, Zhang Z, De Geest BG, Hoogenboom R. Poly (N-isopropylacrylamide) coated gold nanoparticles as colourimetric temperature and salt sensors. Polym Chem 2016; 7(9):1705–1710, with RCS permission.)

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Fig. 1.6 Synthesis of B-ala-based polybenzoxazines.

polybenzoxazine nanofiber nanocomposites were more stimulated by using potassium hydroxide to prepare polybenzoxazine nanofiber nanocomposites and later carbonized at 850°C under the influence of nitrogen atmospheric flow to achieve the activated Fe/CNFs nanocomposite. However, several types of pollutants like organic dyes are found in water sources, which can be treated successfully using carbon-based nanomaterials. However, the sorbent-based separation from water (treated) still remains a challenge.

H3C

CH3

In situ polymerization

H3C

CH3

N N

O

OH

n

230⬚ C curing in vacuum

KOH activation

Poly(BA-a)NF

PVBNF 850⬚ C in N2

A-Fe@CNF : PVB

A-poly(BA-a)NF : Carbon

: Fe(acac)3

: Fe3O4

: KOH

O: Mesopore

Fig. 1.7 Graphic demonstration for the approach by using in situ benzoxazine polymerization to prepare Fe/CNFs composites. (Reproduced from Si Y, Ren T, Ding B, Yu J, Sun G. Synthesis of mesoporous magnetic Fe3O4@carbon nanofibers utilizing in situ polymerized polybenzoxazine for water purification. J Mater Chem 2012;22(11):4619–4622, with RCS permission.)

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1.3.3 Data storage devices Smart polymeric composite materials play a significant role in preparing data storage devices. Information and communications technologies, further precisely data storing strategies, have enhanced remarkably in the past several years. This has helped in the fabrication of novel, smart, polymeric materials such as data chip, USB, etc. However, the holographic data storage will lead to growth to the subsequent generation of information storage devices [75]. They have high storage volume and high rate of transfer as compared with definite 2-D visual disks. In view of this point, azobenzene chromophores were used to introduce optical anisotropy property when combined with photo-addressable polymer materials. Poly(butylene succinate)-poly(e-caprolactone)/multiwalled carbon nanotubes (CNTs), polyurethane (PU)/ sulfonated reduced graphene oxide/sulfonated CNT and poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP)/graphene oxide (GO), etc. are the commonly used composites in energy storage devices [76].

1.3.4 Cancer therapy and surgery devices The smart polymeric material offers a vital status in the fabrication of novel medicinal devices for the diagnosis and treatment of cancer cells. According to this view, magnetic nanoparticles have been used significantly in the growth of hyperthermia behaviors, cellular labeling, magnetic separation, magnetic resonance bioimaging, and immunoassay. The biosensors also depend on smart polymeric composites, which have been used in scientific and medical analyses due to modifications in the absorption of firm analytes such as glucose levels in diabetes and some physical variables. Actuators and biosensors combined in exclusive therapeutic plans such as glucose-sensing and insulin-delivery through several types of medical devices. Microfluidicbased therapeutic devices such as lab-on-chip are also associated with biosensors to sense universal stages of sure actuators and analytes to discharge bioactive mechanisms in response to extreme or inadequate absorptions of the analytes [51]. The temperature-sensitive smart polymers and further specific shape-memory polymers have been used in the fabrication of several surgical medical devices. The exclusive properties of temperature-sensitive smart polymers permit the incorporation of the therapeutic device, they show promising results once situated in the required place. The development of these kinds of material stents is promising for urologic or vascular procedures. Polymer stents are more capable as compared to the traditional metal-based stents due to their unique properties but the prospect of

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integrating a medicine to be eluted, e.g., to decrease thrombosis and restenosis after establishment of the vascular stents and to minimize contamination as a result of placing urinary stents [43, 64].

1.3.5 Drug delivery system Living systems respond to exterior stimuli by reacting and familiarizing to varying external circumstances. Smart polymers have exposed potential for biomedicine applications and are also used as controlled, activated, and selected drug delivery systems, in tissue engineering, cell culture chains, bio-separation devices, biosensors, and as artificial muscles. The concept of smart polymer-based drug delivery schemes was initially described in the late 1970s with application of heat-sensitive liposomes to discharge the drugs through hyperthermia. Subsequently, an excessive deal of investigation has been achieved on smart polymers for drug delivery, particularly on their application and design [77]. The design of novel approaches essentially encounters the challenges accompanying with the management of a good physique. The systems should be simply managed, accomplished of distribution to the wanted sites, biocompatible, made up of toxic free and biodegradable mechanisms. A diversity of smart polymeric materials has been employed in several types of applications, with cross-linked gel systems, and noncross-linked slab copolymer structures. One class considered as most important is smart polymers which significantly used to measured drug deliveries is cross-linked polymer systems such as microgels and hydrogels. The hydrogels have been proved a valuable for a wide diversity of biomedicinally applications due to porous-based structure and water solubility. The porosity allows drugs loading on gel medium and consequent drug discharge at dependent rate on constant diffusion of nano-molecule or macromolecule in network system of gel. Furthermore, several hydrogels can modify their swelling ability degree rate in feedback to fluctuate in their atmosphere. According to hydrogel properties and the mostly used as effective drug deliveries. In case of drug delivery, micro-needles recover drug absorbency into membrane by offering a strong entry path; this advances the performance of deliveries of inoculations and medicinal agents such as protein, DNA and small molecules [78]. The smart polymer nano-carriers for different types of medication deliveries applications show a significant role in the progress of vastly vigorous and careful treatments, allowing a measured delivery of the medicine in the true site at the precise instant. Similarly, Zhang et al. [79] studied the multifunctional nanocarriers by

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Fig. 1.8 Application of smart polymers composite in medicines and biotechnology field.

employing the thermo coupling polymer nanocomposite (poly[(N-isopropylacrylamide)-co-(methacrylic acid)] (P(NIPAm-co-MAA)) composite with mSiO2). This smart polymeric nanocomposite can be served as bio-imaging mediators and bio-monitors to follow the range of drug discharge. The stated multifunctional nanocarriers signify an innovative and multipurpose class of stage for instantaneous bio-imaging and for drug delivery. Several uses in the field of biotechnology and biomedicines are shown in Fig. 1.8.

1.4 Future perspectives The multidisciplinary exploration concerning very diverse disciplines will be essential to offer advances in smart polymer nanocomposite and their several types of application. Polymer chemists, organic/inorganic chemists, material scientists, ecologists, pharmacologists, and therapeutic specialists will have to work together toward realizing innovative materials to meet the requirements of the emerging modern civilization. This aspect advances the superiority of life from a therapeutic view but it is also very significant for data storage, food industry, architectural, and bioenergy storage fields. Therefore, smart polymer-based composite materials have been recognized

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for eras, but it was not fully explored till recently. However, the environmental and biological applications of smart polymer composites are very stimulating and endless. The extensive use of smart polymeric materials include biosensing, cancer therapy, drug delivery approaches, adsorption method, photocatalysis degradation of pollutants, and other toxic pollutant detection and sensing [80]. The most important example of a smart polymer is polybenzoxazine with its several applications. One of the upcoming guidelines of the study in this zone should be to develop polybenzoxazine-based nanocomposites with other materials such as conductive polymers, metal oxide, etc. In the future, merging smart polymer materials with living systems and nano-range materials, a diversity of innovative properties and functions will be available. This growth needs to be maintained through novel concepts that can explain novel behavior like development of innovative smart materials that can be complete to encounter the requirements of a precise application. Another major challenge is to make a novel structure that reacts with several exterior stimuli in several ways. These resources are essential to sustain the growth of biomimetic schemes with extensive durability and stability [81]. However, the nanosized composite material of smart polymer systems brings also a great revolution in the development of much useful stuff for human beings. However, the investigations about the interactions between nanoparticles and the host polymers are still essential, such as how the polymeric parameters affect the distribution and dispersion of nanoparticles. Scientific community must provide significant mechanism to improve the nanocomposite material of smart polymers. Further complete presentation of smart polymer composite applications and values can be accessible from the mentioned reference articles.

1.5 Conclusion Polymeric materials are considered for their applications as stationary physical parts. In recent times, progressive polymeric materials show superior functions with respect to external environments. This may attract more consideration due to a behavior similar to living intelligence noticed in nature. Therefore, these kinds of exclusive polymers are known as stimuli-responsive polymers or smart polymers. Multidisciplinary investigation involving researchers of diverse disciplines will be mandatory to make future developments in the field of smart polymer synthesis and applications zone. Material engineers, polymer chemists, organic chemists, physicists,

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pharmacists, biologists, and medical specialists will have to work together. The developing novel materials such as smart polymers will advance the superiority of natural life, not only in the therapeutic zone, but also in the zones of food, biosensors, textiles, information transformation, data storage, etc. Smart polymers have been produced by using various methods and have been used for many applications. In the future, merging smart polymers with living systems, and nanorange scale resources, will open up a variety of innovative functions and properties. This progress wants to be maintained by new concepts that can define the newly developed behavior such that the growth of innovative resources can be completed in a smart manner to encounter the needs of a definite application. One more challenge is, to progress the systems that react to multiple exterior stimuli in an “intelligent” and expectable manner. These resources are essential to sustain the progress of biomimetic structures with long-lasting stability and excellent durability.

Acknowledgments This study was financially supported by Universiti Sains Malaysia, 11800 Penang Malaysia under the Research University Grant; 1001/PKIMIA/8011070).

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CHAPTER TWO

Manufacturing and design of smart polymer composites Saba Farooqa, Zainab Ngainia, and Sana Farooqb

a Faculty of Resource Science and Technology, Universiti Malaysia Sarawak, Kota Samarahan, Sarawak, Malaysia b Department of Biotechnology, Lahore College for Women University, Lahore, Pakistan

2.1 Introduction Smart polymer (SP) is a polymeric sensitive material which is highly sensitive toward stimuli variations especially for environmental parameters, with unique ability to return to the original state. Smart polymeric nanocomposites are also known as stimuli-responsive materials or intelligent materials [1], smart biomaterials [2], or environmentally sensitive polymers [3]. SP is altered according to the slight change in environmental, chemical, biological, and physical factors such as humidity, UV radiation, pH, temperature, heat, intensity of light, and electricity [4–7]. The first smart polymer was designed in 1988 from electro-rheological (ER) fluids to detect viscosity variations from electrical stimuli response [8]. Various kinds of smart polymers exist such as self-healing [9, 10], hydrogels [11], enzyme-responsive [12], magnetic-responsive [13, 14], photoresponsive [15, 16], pH-responsive [4], shape-memory [17], or stressresponsive [18], electric-responsive [19, 20] and temperature-responsive [21, 22] shape memory composites [23]. SP displays many other fascinating applications such as anticounterfeiting [24], nano-coating [25], optical data storage [26], smart solar cells electronics [27, 28], medical devices [29], robotics [30], drug delivery [31], food packaging [32, 33], biotechnology [34], and bioseparation [35]. Even though SPs have complicated nature or design of structures, poor biocompatibility, and low ability for stimuli detection [36], SPs have sensitive ability to analyze the external variations [37, 38]. Current demand is to amend their nature to enhance their biocompatibility and biodegradability [39] and reduce toxic condition [40] to entertain humankind with its excellent applications [41]. Smart Polymer Nanocomposites https://doi.org/10.1016/B978-0-12-819961-9.00003-7

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2.2 Synthetic techniques Designing a unique style of SPs with high functionality and properties (i.e., controlled size, structure shape, composition, and purity) for specific applications is very challenging. The SPs have been designed via top-down and bottom-up techniques [42] (Fig. 2.1). A small number of distinctive physical designs/shape of SPs can be achieved by using both techniques. The growth rate of kinetics to form a cluster is based on growth and nucleation process to provide varieties of SPs (Fig. 2.2). One of the interesting and demanding shapes is thin-film achieved by a thin layer deposition technique, which is a convenient way

Cluster

Atoms

Bulk

Top Up

Bottom Up

Nanoparticles

Powder

Nanoparticles

Fig. 2.1 Top-down and bottom-up approaches. (© from Oriental Scientific Publisher.)

Nanocomposites Palicated Sphere Hollow Sphere

Nanoplate

Multiroom-Hollow

Yolk-Shell

Dense Sphere Thin film

Core-Shell

Nanowires

Fig. 2.2 Multiplicity of SPs designs. (© with permission and adaptation from RSC.)

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Fig. 2.3 Variety of deposition patterns for nanomaterials (© with permission from RSC.)

for the coating process on the substrate to design thin films of the material of specific size plus thickness of atoms. A variety of SP deposition patterns in solution is depicted in Fig. 2.3 [43].

2.2.1 Top-down technique Top-down technique involves the formation of SP via breaking or successive slicing of bulky materials into smaller reasonable particles using physical or external forces [44]. Solid raw materials required for this further physical processing techniques such as lithographic technique (i.e., electron beam lithography and photolithography) and mechanical technique (i.e., cutting, etching, grinding, and ball milling). Henceforth, most of these top-down techniques are based upon various fabrication forms formation instead of the designing of nanostructured materials. The classic top-down techniques are grinding, crushing, devitrification, milling, and plastic distortions [45]. Many physical, chemical, mechanical, and biologically modified methods updated top-down technique to form unique SPs. The synthesis of SPs can be achieved through controlled experimental conditions (e.g., temperature, flow rate, humidity, pressure, catalyst, and substrate nature, etc.) for size, shape, geometry, and morphology must be chosen wisely. This technique is based on high-energy ball milling, wire explosion, arc discharges [i.e., direct current (DC) or alternating current (AC) arcs], inert-gas condensation (IGC), laser ablation, and ion sputtering [46]. Top-down method is beneficial for large-scale production without any chemical purification and deposition on large materials is possible. Unfortunately, it is too tough to control deposition parameters due to broad size and varied shape of SP distributions (Table 2.1).

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Table 2.1 Advantages and disadvantages of top-up and bottom-down approaches. Properties Top-down Bottom-up

Production scale Size distribution Shape/geometry Cost Deposition parameter Chemical purification Impurities

Large Broad (10–1000 nm) Varied Expensive Difficult to control Not required

Small Narrow (1–20 nm) Ultrafine Cheaper Easy to control Required

Imperfection, defect and stress possible Avoided

2.2.2 Bottom-up technique The bottom-up technique is the formation of SP from bottom, atom by atom, chemically organized from liquid phase [47]. This technique is important for the formation of well-controlled nanocomposite materials through the self-assembly of atoms to form a cluster. This cluster further combines to form self-assembled monolayers on the substrate surface. A variety of raw materials in liquids, gases, and solids has been used for this technique. The SP could be designed using bottom-up technique can be via numerous physical methods [i.e., physical vapor deposition (PVD), evaporation, sputtering, plasma arching, and laser ablation], and chemical methods [i.e., chemical vapor deposition (CVD), PECVD, RF-PECVD, MPECVD, electron deposition, sol-gel method, pyrolysis, and microemulsion route]. This technique provides many advantages by maintaining SP size to achieve outshining crystallinity, homogeneity, porosity, and better physical properties. This technique is capable of controlling the particle and distribution size, which cannot be controlled by physical method. Few methods such as hydrothermal, coprecipitation combustion route, and sol-gel methods are used to enhance the porosity of nanoparticles [45]. Bottom-up technique offers more advantages over top-down due to the formation of fine and ultrafine nanocomposites under controlled deposition conditions. Nevertheless, purification is required and it is harsh to use this method for large-scale production (Table 2.1).

2.3 Synthesis of SP The synthesis of SP can be carried out via chemical, biological, and physical methodologies [42, 48] (Fig. 2.4). The chemical methodology is more efficient due to easy preparation at low temperature. The usage of

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Fig. 2.4 Types of SP methods.

toxic chemicals as stabilizing agents and reducing agents, nevertheless, is able to reduce its stability. The production of harmful nanocomposites is not appropriate for remedial applications [49]. Currently, the formation of SPs via biological methods has gained more attention due to low radiations and less use of toxic chemicals. This is the green synthesis of SP, which is based on economical and environmentally friendly protocol to prepare stable nanoparticles from plant extract (i.e., leaves, roots, stem, and fruits), microorganisms (fungi, bacteria, and yeast), enzymes, and agricultural waste. This method has been used for metal-based nanocomposites, normally capping agent derived from plant materials to form stabilized SPs [42]. Physical methods have few limitations such as the requirement of high pressure, temperature, and radiation. It requires an excess amount of energy and time. Mechanical methods are commonly reported for the preparation of SP. Mechanical methods consist of two methods (i) mechanical blending and (ii) grinding mill. The properties of both methods are tabulated in Table 2.2 [47].

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Table 2.2 Comparative analysis of mechanical blending and ball mill methods. Mechanical Properties blending Ball mill

Homogeneity of nanocomposites Interface reaction Fineness of particle shape, size oxidation and density Deposition and feeding Interface bonding b/w reinforcement and matrix Operational quality

Less Missing Tough to control

High Existing Controllable

Difficult Poor

Effective Strong

Low cost, easy but less efficient

High cost, complex but highly effective

2.4 Synthesis via physical method 2.4.1 Mechanical blending Blending is a convenient method for the mixing process of different types of polymers [50]. The process involves blending either in solution [51, 52] or in dry condition, namely via melt blending [53, 54]. Melt blending is a mixing of reactants such as graphene and polymer in a heated screw mixer and heated source to form liquid melt polymer. The melted material is a designed nanocomposite produced via secondary processing namely blown film molding, injection molding, impression molding, and extrusion [55, 56]. Melt blending techniques is suitable for insoluble polymers [57] such as PC/CO nanocomposites [58], NR/NBR with carbon black and nanosilica [59], polymer/layered silicate [60], MTM/poly(vinyl alcohol)/CNF [61] and PCEGNT (PC/EMA/graphene nanotubes) [62]. This procedure is rapid and has more advantages compared to conventional mixing. The shape memory of PLA/TPU compositions, for instance, can be obtained from twin-screw micro-compounder via melt blending [63] (Fig. 2.5). Shape memory polymers (SMPs) have significant applications in biomedical, aerospace fields [64], and construction engineering [65] due to outstanding espousing nature one (dual-shape), two (triple-shape) or several (multishape) stable temporary shapes, which recover to their original shape (permanent) after removing external stimulus. The external stimulus may be mechanical load, chemical environment, and temperature [66]. Solution blending is a direct method to design nanocomposites in a suitable solvent during mixing of polymer and nanotubes. The dispersion of

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Fig. 2.5 Designing of nanocomposites through melt blending. (© SPIE.)

constituents by mixing or solvent evaporation commonly depends on mechanical agitation (i.e., shear mixing, ultrasonication, and magnetic stirring) [57]. Higher molecular weight polymers are less commonly prepared via miscible blends. Nonetheless, the miscibility is regularly achieved through definite intermolecular interactions (i.e., n-bonding, hydrogen bonding, dipole-dipole, ion-dipole or charge transfer interactions) between two components. The miscibility can directly affect the degree of dispersion [67]. Several nanocomposites have been designed via solution blending such as PU/PCL [68], PMMA/PTBAEMA [69], cellulose-ZnO [70], EPDM/ MgAl-LDH [71], chitosan built organoclay [72], PVC/CaCO3 [73], f-xGNPs/sPS [74], EVA/Clay [75] and PMMA-HRG [76] to name a few. Lago et al. (2016) has designed PC/G nanocomposites via blending of polymer and graphene-dispersion in solution [77] (Fig. 2.6). The solution blending provides good dispersion and easy to handle compared to melt blending. The degradation of SP can sometimes occur in melt blending due to high temperature [78].

2.4.2 Grinding mill Grinding mill method is a mechanically efficient, cheap, and simple method to design SPs by deforming solid material via external force. It is a valuable method for mechanochemistry (MC), mechanical milling (MM) and mechanical alloying (MA) [79]. Grind mill method is a better method than chemical and biological methods due to the formation of the desired nanomaterials with excellent porosity and yield. Size of massive materials is reduced by crushing and grinding process through numerous types of mills, e.g., tumbling mill [ball mill, rod mill, autogenous (AG) mill, semiautogenous (SAG) mill] [80–82], conventional mills (rotary cutter mill

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Fig. 2.6 (A) PC/G nanocomposites preparation via solution blending. (B) PC/G composite bits obtained at various concentration of graphene flakes. (© with permission from RSC Adv.)

[83], vibrational mill [84], turbo mill [85], rod mills [86], hammer mill or high-speed pulverizing [87]) and innovative mills (i.e., fluid energy mill or jet mill [88], high power density mill [89], high pressure grinding rolls [90] and ultrafine grinding). Some of these mills are used in the laboratory for the SPs designing such as ball mill (A) [91, 92], planetary ball mill (B) [93], vibrational mill (C), attrition or stirred media mill (D) [94, 95], pin mill (E) [96], and roller mills (F) [90, 97] (Fig. 2.7A). Ball mill is very common and its internal physiochemical mechanistic variations based on elastic deformation, plastic deformation, shear

Fig. 2.7 Varieties of mills used to design nanocomposites (A) and inner mechanistic view (B) of ball milling processing. (© with permission from RSC Baláž P, Achimovic
ová M, Baláž M, Billik P, Cherkezova-Zheleva Z, Criado JM, et al. Hallmarks of mechanochemistry: from nanoparticles to technology. Chem Soc Rev 2013;42(18):7571 and MRS Online Proceedings Library Balema VP, Mechanical processing in hydrogen storage research and development. Mater Res Soc Symp Proc 2010;1209:P01-5.)

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deformation, and fine product formation [98] (Fig. 2.7B). Several factors affected the grinding for example size reduction, ball-filling ratio, wet or dry milling, milling environment (i.e., time, pressure, and temperature), pot depth, ball diameter, pot diameter, rotational speed, and revolution radius [99]. However, it is difficult to observe the grinding progress inside mill and balls movement inside the mill [100]. Grinding method is a top-down method that continuously improved to achieve fine and ultrafine nanocomposite materials. The conventional ballmill modified and remodified to achieve high stress intensity, fine, and smooth grinding, decent operating setting (i.e., less noisy and less dusty), less energy, shorter time, high grinding efficiency, deformation rate, and high capacity to design nanomaterials [95]. Sometimes the iron manufactured ball can cause contamination and reduce efficiency due to high friction while grinding. The explosive materials can cause a fire explosion that can be avoided under inert gas. After multiple unique instrumental developments such as planetary ball mill [101, 102], high-energy ball mill [103, 104], vibrational ball mill [105], high-pressure ball mill [106], shaker mill, inside of milling tank, rotor with a blade, and large-scale high-energy horizontal rotary, high-energy shaker with cryogenic temperature [107] has been reported for improving proficiency. Conversely, the conventional ball mill is still considered efficient, dominant, and preferable as compare to other mills [108]. Mechanical ball grinding method is commonly used on an industrial scale due to higher production rate and shorter time of chemical reaction [109]. Ball mill method with stainless steel balls, lid and capsule is a versatile, homogenous, uniform, nontoxic, and efficient method. This method is frequently used for the synthesis of nanocomposites. High yield and quality of low-priced graphene nano-sheets [edge-selectively carboxylate graphite (ECG)] were designed from dry ice and pristine graphite by using ball mill method which exhibited good electronic applications [110]. Several nanocomposites have been designed such as Al-coated graphene [111], CoCr2O4/carbon [112], CNT/Al [113], CNT/PLA [114], and encapsulated laccase-based nanobiochar-chitosan [115] through ball mill technique.

2.4.3 Physical vapor deposition Physical vapor deposition (PVD) is a bottom-up approach for the generation of nanocomposites through IGC, levitational technique (LG), thermal evaporation, molecular beam epitaxy (MBE), sputtering, and spray pyrolysis ways via simultaneous formation and condensation of vapors [116, 117].

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2.4.3.1 Inert-gas condensation IGC is the most common bottom-up approach to form ultrafine nanoparticles of the desired morphology. Controllable size and good yield can be achieved through flexible and renowned IGC techniques using metallic sources, in the presence of inert atmosphere [118]. This method consists of evaporating, sputtering, and condensation process for the refinement of material inside the chamber. However, this technique has been used to process alloys, metals, carbides, nitrides, oxides, etc. under corresponding inert gaseous atmosphere. Recently, nano-glass has been successfully achieved by this condensation method [119]. Pandya and Kordesh (2015) have successfully prepared the indium antimonide (InSb) nanoparticles through IGC. Condensation and deposition chambers are the main parts of IGC. In condensation chamber, InSb atoms are initially produced via sputtering in an argon atmosphere. Sputtering atoms condense and form clusters, followed by transformation into nanoparticles under vacuum deposited in the deposition chamber [120] (Fig. 2.8). 2.4.3.2 Levitational technique Levitation technique (LT) is an auspicious way to uplift any material at the stable position without additional mechanical support to blend materials in homogenous microstructure and to exclude the difference between components [121, 122]. Example of materials form via LT are cobalt-carbon [123], AlSi10Mg alloy [111], and titanium hydride [124]. Previously, the stimulation process of specific microgravity requires the magnetically levitated droplet melted easily to get nano powder with good physiochemical properties. However, this technique is limited to the conductivity of metallic materials known as electromagnetic levitation [125]. Further techniques have been presented for nonconductive material, for instance, polymer,

(A)

(B)

Fig. 2.8 (A) Laboratory inert gas condensation and (B) NPs formation process. (© from Springer Nature.)

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and organic materials [126]. With the passage of time, this technique is further developed into variety of modified techniques such as electrostatic levitation [127], lavitational gas condensation (LGC) [128], flow levitation [129], ultrasonic lavitation [130], aerodynamic levitation [131], jet-based levitation [132], acoustic levitation [126], and optically levitation [133]. The comprehensive comparison and processing of these techniques have been reported [121] and depicted in Table 2.3. 2.4.3.3 Evaporation Evaporation is a natural process that occurred on the surface of liquids and the most common PVD technique. The substrate (either melts or mixed) is transferred into vapors and deposited on a plate to generate nano-films via numerous sources [142, 143]. Evaporation is the detachment of atoms from surface or surface-breaking process due to the movement of outgoing atoms from the plane of surface, depending on the molecular configuration and intermolecular force. Nanoparticles, which are partially engrossed in a solvent surface, are escaping molecules to the upper layer by reducing the bond energy with low-lying neighboring molecules. Whereas, the floating nanoparticles on the solvent surface gained chances to boost evaporation and variations occurred at the upper layer and contact area between solvent and nanoparticle exposed to ambient. The surface of nanoparticles is only partially covered with some layers of solvent molecules and these few solvent molecules are adsorbed on the surface nanoparticles shown in the upper right [144, 145] (Fig. 2.9). After this process, the nanoparticle moved up to deposit at the target surface. Currently, researchers are utilizing evaporation method to synthesize SP nanoparticles namely Teflon/Nylon with Au/Ag [146], rGO-MWCNT [147], PEO/whisk [148], BaTiO3 NPs@PVDF [149] and CdSe/ZnS quantum dots/PI [150]. The summary of the evaporation process in designing SP is shown in Table 2.4. 2.4.3.4 Sputtering Sputtering is one of the PVD process based on the bombardment or collision of energetic ions with target (cathode) material for the deletion of target ions and deposition on the anode in the presence of rare gas [151]. The mechanism is generally based on the acceleration of target ions, sputter off, and deposition (Fig. 2.10). Numerous advantages of the conventional sputtering method are the highly stable sputtering target and long-standing vaporization source for elements, compounds, and alloys. The reactive deposition of sputtered atoms can be fast, efficient, and easily proficient due to the

Table 2.3 The comparative properties of IGC and LGC. Properties IGC

Approach Inert gas Magnetic field Advantages

Bottom-up Required Not required

LGC

Bottom up and top-down Not required Required

• Flexible techniques to form ultrafine particles of desired • Current modified LGC techniques are useful for conductive size

• Variety of material (alloy, semiconductors, ceramic, • • Drawbacks • • • • •

and nonconductive both materials

• Preventing the coalescence

metallic, etc.) Good yield High purity Expensive • Previous LGC was specific for conductive metallic materials Difficult to scale up • Expensive Tedious vacuum cleaning • Instrumental maintenance is sensitive Agglomeration Sometimes IGC is not suitable for semiconductors, i.e., GaAs and InP due to decomposition issue

Image

Cold finger (77 K)

Ga

IIIIn

Metal feeding part

W High frequency induction generator inductive melting / levitation / evaporation

Ga W Thermal evaporation

IIIIn

Inert gas (Ar)

Sputtering

Reaction chamber condensation and particle cooling

Vacuum pump

Nonopoweder collecting part filtering and injection into solvent Vacuum

Compaction unit

WGa: IIIIn

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Ead Eb

Solvent Surface

Nanoparticles

Fig. 2.9 Evaporation process to design NP, Eb: binding energy of solvent molecule at solvent surface; Ead: adsorption energy of solvent molecules on nanocomposites. (© from AIP Adv.) Table 2.4 Variety of evaporation techniques to design SPs. Evaporation types Advantages Disadvantages

Thermal evaporation [134]

• Low contamination • Controlled deposition rate

Electron-beam evaporation [135]

• Highly cost RF power supply • Poor step coverage • Difficult to control film

• • • High voltage is required • to emit electron from •

composition than sputtering High temperature High vacuum Used for high MP materials High vacuum required

tungsten filament Matrix-assisted laser pulse evaporation [136–139]

Arc evaporation [140] Ion plated evaporation [141]

• Less contamination • Suitable for organic compounds • Various properties controlled such as: • Solvent founded processes faced trouble to form uniform • Thickness films especially on large • Homogeneity surfaces • Roughness • Low temperature • Not available required

• Useful at industrial scale • Latest efficient • Not available • Enhanced purity and deposition rate

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Fig. 2.10 Sputtering process. (© Elsevier.)

presence of reactive gases in the plasma. The space substrate and source can be reduced to achieve a small chamber size. There are, however, some drawbacks of sputtering processes such as slow rate of deposition, expensive target materials, and inadequate energy to heat the material in the sputtering initiation process. In reactive sputtering, handling of gas composition is important to avoid poisoning. Some examples of the sputtering methodology-based smart materials are Au@In2O3 [160] and ZnO thin films [161]. The sputtering deposition is capable to deposit several materials and better than the evaporation method due to this reason it has been developed to achieve desired nanocomposites. The advantages and disadvantages of various types of sputtering techniques are depicted in Table 2.5. 2.4.3.5 Molecular beam epitaxy MBE is a specific technique to design epitaxial films of high quality by arranging precise atoms [162] in PVD. In MBE, the base material is initially heated at specific degrees, followed by gaseous atoms or effusion particle’s beam sprayed through gun. These molecules eventually condensed on surface and formed one atom-based ultrathin layer like thin film deposition. This is highly controlled conditions to monitor crystal growth and contaminations (unwanted dirt particles or gas molecules) especially under ultrahigh vacuum (UHV) [163]. Some other parameters have also affected the growth of crystals such as nature and concentration of substrate, temperatures, and arrays of real-time reflection high energy electron diffraction (RHEED) for in situ evaluation technique to examine the structure of crystal growth [164]. The advantages of this technique are no chemical reaction involved, low

Table 2.5 Various types of sputtering techniques: advantages and disadvantages of. Types of sputtering

Cathode (target)

Cathode Cathode Argon plasma or Anode glow Dark space negative glow sheeth or sheeth

DC/AC sputtering [152]

Disadvantages

• Easily controllable • Charge gained by alternating potential • Cheap method

Wafers

(Ve")

Advantages

Anode

sometimes causes trouble. • Slow ionization or bombardment • Slow deposition • Poor sputtering rate

• Insulating targets

RF Power Input Matching Network

Electrode/Target

RF Generator

• Low ionization enhance activity • Damage of sample due to e-bombardment • High efficiency • Lesser Ar pressure gives more sightline deposition

Argon Plasma Wafers Electrode Heater

Sputtering Gas Inlet (Ar)

Vaccuum

RF sputtering [153, 154] Continued

Table 2.5 Various types of sputtering techniques: advantages and disadvantages of—cont’d Types of sputtering Advantages

• Commercially

Vacuum Chamber Mass Flow Convertor

Substrate Holder Coating Flux

Substrate

Plasma Art Gas

Target

Vacuum pump

Magnetron sputtering [155]

DC or RF Power Supply

preferable sputtering • High deposition rate • Less electron showering required • Operated at vacuum range especially at lower pressure

Disadvantages

• Poor efficiency • Erosion target track • Uneven ejection of target particles give rough films

Target

• Low pressure required

• Less efficient • Poor deposition rate

Wafer Substrate

Collimated Sputtering [156, 157] Continued

Table 2.5 Various types of sputtering techniques: advantages and disadvantages of—cont’d Types of sputtering Advantages

• Less energy ion source • Excellent yield • High quality of smooth film • Less pressure is required

Ion beam sputtering [158, 159]

Disadvantages

• Small target area for bombardment

• Poor deposition rate • Not suitable for largearea film with fine thickness • The device is expensive and complicated too

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Fig. 2.11 (A) MBE growth for the synthesis of thin Bi2O2Se films on SrTiO3 (STO) substrate. (B and C) Crystal assemblies of Bi2O2Se and STO respectively, exhibited slight lattice mismatch in ab plane and same in-plane of the crystal symmetry. (© with permission from Wiley-VCH.)

temperature, and no safety precautions required. However, the maintenance of low temperature is challenging, while the growth rate is slow. Currently, a variety of thin films has been prepared using this technology such as LiNbO3-type MgSnO3 and ZnSnO3 [165], gallium nitride (GaN) [166], GaN nanowires [167], GaN nanorods [168], α-Sn [169], Mg-doping-(111)B GaAs [170], and MoTe2-SiO2/Si [171]. One interesting example is a thin atomic oxychalcogenide of Bi2O2Se/SrTiO3, which was prepared via MBE using thin Bi2O2Se films on monolayer SrTiO3 (001) substrate, by co-evaporating Se and Bi precursors in atmospheric oxygen. The atomic arrangements of Bi2O2Se/SrTiO3 are observed with a sharp interface and atom-to-atom alignment, while electron bandgap of oneunit-cell was thick in Bi2O2Se films [172] (Fig. 2.11). In short, these thin films are good for optoelectronic properties and semiconductor laser to facilitate medical fields such as photodynamic therapy, acne treatment, hair removal, ophthalmology, dental and vascular, liposuction [173]. 2.4.3.6 Spray pyrolysis (aerosol decomposition) Spray pyrolysis is a simple aerosol decomposition, low-cost, and breakdown technique based on thermal degradation of a liquid sample produced via spray pyrolysis [174]. This technique offers considerable preparative parameters to control airflow, spray rate, adherence of substrates, solution concentration, droplet size, volume, gap between the substrate, and spray gun for the desired SPs [117]. Spray pyrolysis is gradually updated to improve the quality of nanomaterials [175]. The current uses of spray pyrolysis techniques are conventional deposition spray pyrolysis, thin film deposition spray

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Fig. 2.12 Spray pyrolysis deposition. (© with permission from RSC.)

pyrolysis, jet nebulizer spray pyrolysis, flame spray pyrolysis (FSP), jet ultrasonic spray pyrolysis, laser pyrolysis, and electrospray pyrolysis [176]. Jet nebulizer spray pyrolysis has three subtypes namely ultrasonic, electrostatic, and pneumatic atomizer. The flame spray is a well-known technique. Many reviews have illustrated the function of the instrument, advantages and disadvantages of the techniques to produce various shapes of SPs [177] (Fig. 2.12). Other nanocomposites prepared via spray pyrolysis techniques are TiO2 nanoparticles [178], NiO-MWCNTs [179], WO3-nanoplate [180], CuO NPs [181], and SnO [182].

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FSP involves the thermal decomposition process, which requires high temperatures and short residence time. Fig. 2.13 depicts the mechanism for the formation of solid nanoparticles via FSP from droplet [185]. Initially, the droplets are achieved by using a nozzle that is evaporated further to transform into gaseous phase by flame. The precursor of gaseous molecular species is burnt and produced a self-sustainable spray of combustion. The decomposition consisted of various reactions called precursor pyrolysis that depends on the nature of precursor moiety and the type of gases used [186]. Metal oxide and metal both exhibited very low-saturation vapor pressure (i.e., 133 Pa vapor pressure is required for zinc at 500°C). Therefore, the obtained gaseous vapors are strongly supersaturated and stochastically firm collisions to make possible formation and deformation of molecular clusters, which depends on nucleation (homogeneous and heterogeneous) and

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Fig. 2.13 Processing of SPs formation in FSP (A) Physical appearance (B) detailed chemical appearance. (© with permission from RSC Advances and Universita€t ErlangenN€ urnberg [183, 184].)

process parameters to achieve aggregation, coalescence, surface growth, and agglomeration. FSP is similar to spray drying and spray pyrolysis with few significant variations. In FSP, a very high temperature [>2700 K (2426°C)] is required for faster droplet evaporation than spray pyrolysis. Spray drying is a simple physical process with temperature 99.5% oil separation efficiency from water for varying concentrations of oil-water feed mixtures with rapid surface switchability and regeneration ability. Further, sustainable biomass-derived activated carbon blended with the PVDF membrane was developed and studied for water desalination applications. The membrane showed reversible desalination and resalination phenomena with a high capacity of 22.5 mg/g for an applied actuation voltage of 1.2 V [68]. Similarly, rapid electrosorption and better recyclability of PVDF

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Fig. 14.15 Schematic representation of ERMs synthesis process. (Reproduced with permission from Du L, Quan X, Fan X, Chen S, Yu H. Electro-responsive carbon membranes with reversible superhydrophobicity/superhydrophilicity switch for efficient oil/water separation. Sep Purif Technol 2019;210:891–9. Copyright 2019, Elsevier.)

membranes reinforced with peanut shell-derived carbon and iron oxide composite for NaCl removal from water by capacitive deionization technique has also been reported [69]. Application of EAPs in a membrane bioreactor to selectively remove the pollutants and prevent the fouling effect was studied using an electrically conducting polypyrrole membrane at an applied potential of 2 V. These electro-responsive membranes showed flux enhancement and fouling resistive behavior as compared to nonconducting membranes [70]. Electro-responsive membranes have gained importance due to their salient benefits, especially with regard to water desalination applications and the development of better antifouling membrane systems. However, the technological system is still in the toddling stage and yet has to be intensively researched. The concepts are still in the lab-scale, and no long-term results have been published yet. One of the main challenges with regard to electro-responsive membranes is the stability of the electro-responsive carrier group in the polymeric matrix, especially when they are applied for high-pressure filtration as well as wastewater treatment containing toxic chemicals. Another challenge is the cost, while the perfect engineering design for the membrane module is also greatly debated. All these factors pave the way for in-depth research with regard to electro-responsive membranes and its application for water and wastewater treatment.

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14.6.2 Magnetic-responsive membranes Of late, the concept of stimuli-responsive membranes has kindled the interest of researchers for the study of new kinds of membrane materials which can show property changes under the application of new stimulating agents. Specifically, attempts are made to produce strong antifouling membranes for applications like water and wastewater treatment, in which membrane fouling plays a very crucial role in the determination of filtration performance and the life span of the membrane system. One such interesting category of stimuli-responsive membranes is magnetic-responsive membranes (MRMs). These membranes are exclusively studied for the development of antifouling membranes, which can be mainly applied for wastewater treatment systems. Pristine polymeric or composite polymeric materials have been widely studied for the synthesis and application of magneticresponsive membranes. The core concept of such membrane types lies with their ability to undergo pore enlargement or shrinkage under the influence of the magnetic field. The shrinkage effect improves the rejection efficiency of the membranes, while the pore enlargement functionality can help in the regeneration of the fouled membrane surface by backwashing. Remarkably, the irreversible fouling effects due to internal pore wall blocking can be removed to a greater extent in the case of magnetic-responsive membranes. Synthesis of MRMs mainly consists of the inclusion of iron and iron composites in the polymer matrix. Poly(2-hydroxyethyl methacrylate) grafted polyamide blended with supermagnetic Fe3O4 nanoparticles was used for the production of a magnetic-responsive NF membrane. The membranes showed higher rejections and decreased flux for CaCl2 and MgSO4 salt separation studies under the influence of the magnetic field [71]. UF membranes developed using a PES substrate and incorporated with PEG and iron oxide nanoparticles were applied for dye rejection studies. The composite PES/PEG/Fe3O4 membranes showed a 400% increase in permeate flux with almost the same retention as compared to the control PES membrane [72]. Defluoridation of groundwater for drinking applications was performed using a PES/cellulose acetate blend membrane modified with iron oxide particles. The magnetic iron oxide particles regulated the pore size of the resultant hybrid membrane. Maximum pure water flux of 156 L/m2 h with a high defluoridation efficiency of 70.3% was achieved for the membrane under the influence of the magnetic field [73]. Additionally, studies on metal ions filtration present in wastewater were carried out using a magnetic-responsive PES/iron nanoparticle composite membrane.

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100 ppm F-MNPs membrane (Ms = 0.68 emu/g)

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The enlarged pore size under the presence of magnetic fields showed increased permeate flux with an agreeable reduction in the metal ions rejection efficiency [74]. The development and analysis of better antifouling membranes using iron/iron oxide intercalated cellulose acetate membranes have also been reported [75, 76]. Further, ferrogels—a special category of hydrogels composed of colloidal dispersion of magnetic nanoparticles—have also been incorporated in the polymer matrix and studied for various applications [77, 78]. The effect of magnetic field on permeation flux is depicted in Fig. 14.16. In addition to these water treatment applications, MRMbased membranes are also used in pharmaceutical and biological applications for targeted drug delivery control and selective separation of proteins, amino acids, biological strains, etc.

14.6.3 Ultrasound responsive membranes Ultrasound responsive membranes (URMs) are a very recently emerging class of stimuli-responsive membranes, wherein the membrane

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characteristics are altered through ultrasound applications. In general, most of the membrane properties such as surface wettability, pore morphology, charge nature, etc. are related to the functional end groups and bond nature of the polymer matrix. The ability of ultrasound to tune these end groups and bond nature of the polymer backbone results in a different set of filtration properties for the same membrane material. URMs are mainly used in biomedical applications such as cell sensing, drug delivery, protein engineering, and tissue transport. The research quantum for the usage of these sound responsive membranes for water treatment is feeble and thus presents a large scope for examining these URMs for water and wastewater treatment. URMs are mainly classified based on the intensity of the sound field applied as: (i) low-frequency URMs (