Metal Oxide Based Nanomaterials and Their Polymer Nanocomposites

Metal Oxide Based Nanomaterials and Their Polymer Nanocomposites

CHAPTER 4 Metal Oxide Based Nanomaterials and Their Polymer Nanocomposites S.R.V. Siva Prasanna*, K. Balaji†, Shyam Pandey*, Sravendra Rana† * Depar...

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Metal Oxide Based Nanomaterials and Their Polymer Nanocomposites S.R.V. Siva Prasanna*, K. Balaji†, Shyam Pandey*, Sravendra Rana† *

Department of Mechanical Engineering, University of Petroleum and Energy Studies (UPES), Dehradun, India Department of Chemistry, University of Petroleum and Energy Studies (UPES), Dehradun, India

4.1 INTRODUCTION Various metal oxide-based nanomaterials and their polymer nanocomposites have been reported over the decades. Due to their outstanding properties, such as electrical, magnetic, mechanical, optical, catalytic, etc., metal-oxide based nanomaterials are playing an important role in a wide range of applications including gas sensors, fuel cells, advanced ceramics, chemical sensors, biosensors, batteries, solar cells, pyroelectric, super capacitors, catalysts, anticorrosion coatings, etc. (Corr, 2013; Dar, 2015). A series of metal oxide nanoparticles have been synthesized including TiO2, SiO2, iron oxide, zinc oxide (ZnO), gallium oxide (Ga2O3), nickel oxide (NiO), copper oxide (CuO), etc. They have different morphologies such as spherical, triangular, star, nanowires, nanotubes, nanorods, etc. Due to a high density and limited size, metal oxide nanoparticles showed exciting results in terms of physical and chemical properties; therefore it is highly desirable to understand their various aspects in terms of synthesis, properties, and applications. In order to prepare polymer-metal oxide nanocomposites with a nanophase-separated structure, the homogeneous dispersion of metal oxide nanoparticles including a reduction in the size of the polymer-metal oxide interface is very important as it essentially alters the physical property of the nanocomposites. It is a crucial to have a homogenously dispersed metal oxide throughout the polymer matrix in order to form a homogeneous nanophase separated structure. Due to the presence of metal oxide nanoparticles the properties of polymer nanocomposites can be improved. In general, properties including thermal stability, toughness, glass transition temperature, optical, tensile strength, etc. are found to be improved by the formation of such nanocomposites with different polymer matrices. Thus these nanocomposites are widely used in different applications, from active surface coating to biomedical applications including structural materials. Due to vast number of publications on the synthesis of metal oxide/polymer nanocomposites, it is difficult to cover the topic completely; therefore this chapter will provide a general overview of the basic strategies involved in the synthesis of metal oxide

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nanoparticles, including the advancements in metal oxide-based polymeric nanocomposites and the evaluation of their properties.

4.2 SYNTHETIC STRATEGIES The synthesis of metal oxide nanomaterials with a desired composition and morphology is one of the most challenging tasks. Due to their novel properties the synthesis of metal oxide nanomaterials has inspired great interest, which is helpful in fabricating efficient devices applicable from electronics to composite materials. Various synthetic strategies for the production of metal oxides based on different techniques, including physical vapor deposition (PVD), chemical vapor deposition (CVD), chemical processes, etc. are discussed in the following subsections.

4.2.1 Physical Vapor Deposition PVD is a technique that involves the evaporation of the source material above its melting point in a closed chamber, where the evaporated particles go straight and get deposited on the substrate due to the free path created by a vacuum. Thermal Evaporation Thermal evaporation is one of the oldest and simplest methods used for the synthesis of metal-oxide nanomaterials (Henini, 2000). This technique requires a high temperature thermal furnace used for vaporizing the source materials and facilitates the deposition of the nanostructures with thicknesses ranging from Armstrong to microns (Savale, 2016). This method allows control of parameters such as uniformity, thickness, adhesion strength, grain structure, stress, electrical, and optical properties (Campbell, 2001). Even though thermal evaporation is simple in operation, additional components such as source containers, auxiliary for vacuum pressure, process monitoring, and substrates for precise control of uniformity (Corr, 2013) are required for a smooth operation. Pulsed Laser Deposition Pulsed laser deposition (PLD) is a type of PVD in which a laser having a high-power density and narrow frequency bandwidth is used as a source for vaporizing the desired material. In particular, this technique is used where other techniques have been problematic or have failed to make the deposition (Willmott and Huber, 2000; Ashfold et al., 2004; Buzby et al., 2006) and has been used to synthesize the nanotubes (Zhang et al., 1998), nanopowders (Geohegan et al., 1999), and quantum dots (Goodwin et al., 1997). The versatility of PLD is that there is almost no restriction on the target material to be used. Matrix assisted pulsed laser deposition is used for hybrid metalorganics, coordinative and complex compounds, biomaterial, and polymers (Lippert et al., 2007). The thickness of deposition material is in the range of 10–500 nm on

Metal Oxide Based Nanomaterials and Their Polymer Nanocomposites

different substrates. PLD was reported for the synthesis of titanium (TiO2) nanoparticlebased film applicable for the preparation of a gas sensor (Rella et al., 2007), where synthesized nanoparticles 10 nm in diameter were obtained (Fig. 4.1) (Caricato et al., 2007). Sputtering Deposition Sputtering deposition composes the vaporization of a solid via sputtering with a beam of inert gas ions. This technique is used in various applications such as the deposition of oxides in semiconductors, head surfaces, magnetic media, cutting surfaces, coating tools for wear resistance, etc. The formation of various metal oxides using magnetron sputtering of metal targets was achieved by Urban et al. (2002), in which the researchers formed collimated beams of the nanoparticles and deposited them as nanostructured films on silicon substrates. This method has been used for the synthesis of variety of nanostructures like ZnO, W, Si, B, CN, etc. (Cao et al., 2001, 2002; Karabacak et al., 2003). Tvarozek et al. (2007) fabricated the p-type and n-type zinc oxide films using the plasma-assisted sputtering. This approach allows for the interaction of ions and ion complexes and deionizes the energetic atoms and electrons with a growing film. The authors have also focused on depositing the ZnO and ZnO:N on the silicon wafers that contain the silicon oxide layer (0.8 μm) and glass substrates. The results obtained in terms of thickness were found directly dependent on the sputtering time and power. Molecular Beam Epitaxy Due to its unparalleled ability to control the layering at the monolayer level and its compatibility with surface-science techniques to monitor the growth process, molecular

Fig. 4.1 Morphology of TiO2 using AFM in two- and three-dimensions. (Reprinted from Caricato, A.P., Manera, M.G., Martino, M., Rella, R., Romano, F., Spadavecchia, J., Tunno, T., Valerini, D., 2007. Uniform thin films of TiO2 nanoparticles deposited by matrix-assisted pulsed laser evaporation. Appl. Surf. Sci. 253, 6471–6475 with permission from Elsevier.)



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beam epitaxy (MBE) is useful in synthesizing the semiconductors as well as metals and insulators metal oxide nanoparticles. It is a vacuum deposition method in which welldefined thermal beams of atoms or molecules react at a crystalline surface to produce an epitaxial film, which can be characterized in situ during growth. Despite higher technological costs, epitaxial technologies have been used to grow the oxide superconductors YBa2Cu3O7 δ, (Berkley et al., 1988), (Pr,Ce)2CuO4 (Naito and Sato, 1995) and Bi2Sr2Can1CunO2n+4 for n ¼ 1–11 (Klausmeier-Brown et al., 1992; Schlom, 2015). The technique has also been used to grow ferroelectrics including BaTiO3 (McKee et al., 1991, 1994) and the incipient ferroelectric SrTiO3 (Bozovic et al., 1994); the ferrimagnet Fe3O4 (Chambers, 2000); etc. Due to the absence of highly energetic species during deposition, MBE is the method of choice when it comes to achieving the intrinsic properties of sensitive materials. For example, EuTiO3 is an antiferromagnet on the verge of becoming ferromagnetic. To date the only technique that has succeeded in achieving this antiferromagnetic ground state in as-grown films is oxide MBE (Lee et al., 2010).

4.2.2 Chemical Vapor Deposition The CVD process involves gases or precursor gases passing toward one or more heated substrates, where the chemical reactions occurs near the surface of the substrate to form a solid deposit. It is accomplished byproducts releasing during the chemical reaction through the exhaust chamber. The total process is performed in a temperature range of 200–1200°C using different energy sources such as lasers, electrons, photons, ions, plasmas, and hot filaments. The physical properties of a deposited film are strongly affected by crystallinity, growing structure and nucleation (Polarz et al., 2005). The synthesis of zinc oxide nanoparticle with high purity using CVD has also been reported by Polarz et al. (2005). The authors found that [CH3-ZnO-CH-(CH3)2]4 of heterocubane cluster is the most suitable precursor for producing ZnO nanoparticles, where the decomposition was achieved through the elimination of methane and propane. The primary particles get aggregated and forms large particles due to the formation of the Zn4O4 cluster. Amara et al. (2012) reported the synthesis of magnetite nanoparticles using the traditional CVD technique. The authors had fabricated the magnetite nanospheres and nanocubes on the poly(vinyl pyrrolidone) (PVP) substrate using ferrocene as the precursor. The particle growth was governed by the formation of PVP and iron complexes. From the observations it was found that particle size was influenced by the annealing time and PVP concentrations (Fig. 4.2).

4.2.3 Chemical/Solution Process A number of chemical/solution processes are routinely employed to obtain a large variety of metal oxide nanomaterials. A few of those are presented below.

Metal Oxide Based Nanomaterials and Their Polymer Nanocomposites

Fig. 4.2 Electron micrograph of PVP with 1:2 ratio at 350°C for 2Hr (A and B) or 4 h (C and D). (A) nanocubes, (B) ED pattern, (C) nanospheres, (D) ED pattern. (Reprinted from Amara, D., Grinblat, J., Margel, S., 2012. Solventless thermal decomposition of ferrocene as a new approach for one-step synthesis of magnetite nanocubes and nanospheres. J. Mater. Chem. 22, 2188–2195 with permission from Royal Society of Chemistry.) Sol-Gel Approach The sol-gel process is generally used for the fabrication of metal oxide nanoparticles at elevated temperatures by using metal alkoxides or colloidal dispersions with the intermediate route like sol and gel states. It includes multicomponent oxides that are homogeneous at atomistic level (Hench and West, 1990). Generally, there are two basic possibilities for formation gel: (a) the dispersion of particles in a liquid forming solid or network using different mechanisms; or (b) the formation of molecules by polymerization (Brinker et al., 1992). A single-step synthesis of iron-oxide silica nanocomposites in the presence of tetraethylorthosilicate (TEOS) was achieved (Zhang et al., 2007), where initially the iron alkoxide precursor [Fe(OBut)2(THF)]2 was hydrolyzed in water by providing ultrasonic irradiation in the presence of TEOS. The concentration of TEOS plays a crucial role in controlling the shape and size of the particle; at lower concentrations, it is easy to form spherical particles, whereas higher concentrations favor the formation of nanorods.



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An inverse microemulsion technique was also applied to synthesize the Cu-doped ZnO nanoparticles with excellent bactericidal properties (Liang et al., 2012). Initially the Cu-doped ZnO nanoparticles were prepared using the sol-gel process. As the first step, the metal nitrates were dissolved in water followed by the addition of citric acid and ammonium solution. This solution gave the gel formation when it was heated and dried. The advantage of using this process is that it can be used for all types of oxide composition, as well as for the fabrication of new hybrid materials related to organic and inorganic materials. The nucleation and growth of particles are easily controlled in order to provide the proper size and shape. The important limitation of this process is that it is not economical, as it requires costly precursors and alkoxides. Coprecipitation Microemulsion coprecipitation is a bottom-up synthetic approach for the metal oxide nanomaterials production, where pH, viscosity, surface tension, temperature, concentration of solution, and stirring speed are the major parameters for controlling the properties of the product. Normal and reverse are two possible types of micelles that get generated during the process. In the normal micelle reaction, spherical micelles form in water; thus the hydrophilic end of the surfactant extends into the water. However, in case of a reverse micelle approach the water droplets form the micelles, and the hydrophobic end of the surfactant is oriented into the organic phase. A large amount of waste production including a low production yield limits the use of this technique (Gaikwad et al., 2006). Solvothermal Approach Using this technique a material undergoes a chemical reaction in the presence of a solvent in a closed chamber under high pressure and temperature (higher than the boiling point of solvent). (Demazeau, 2008). The solvent plays a crucial role in the solvothermal process (Ye et al., 2011), which synthesizes mesocrystal TiO2 by using tetrabutyl titanate as a base material and acetic acid as the solvent (Fig. 4.3). The treatment started at 200°C for 24 h, whereas the calcination started at 400°C for removing the residuals, resulting in metal oxide nanoparticles 280 nm in diameter. By using the solvothermal/hydrothermal processes, it is easy to control the particle size and shape by varying the thermodynamic and chemical parameters. Biomimetic Approach Researchers have been seeking alternative methods to passivate not only the rate of waste production, but also the cost of spending for the fabrication of a rapid prototyping technique, which is essential during metal oxide particle synthesis. The traditionally production of these devices (e.g., CVD, laser ablation, photolithography, etc.) has been achieved at a high price, under harsh (i.e., high temperature) reaction conditions, and a surplus in generated waste (Hwang et al., 2015; Prathna et al., 2010). Inspired by a natural/biological

Metal Oxide Based Nanomaterials and Their Polymer Nanocomposites

Fig. 4.3 Scheme for the formation of TiO2 using the solvothermal process. (Reprinted from Ye, J., Liu, W., Cai, J., et al., 2011. Nanoporous anatase TiO2 mesocrystals: additive-free synthesis, remarkable crystallinephase stability, and improved lithium insertion behavior. J. Am. Chem. Soc. 133(4), 933–940 with permission of Journal of American Chemical Society.)

process the synthesis of highly ordered nanostructures have been achieved successfully. The approach encompasses alternative approaches toward the development of nanomaterials with technological applications (Bello et al., 2013). The valuable properties associated with constrained or unconstrained metal oxide synthesis in specific biological systems has inspired the development of functionalized nanomaterials; for example a mixture of manganese chloride tetrahydrate (MnCl24H2O) and PAA immediately formed a clear orange liquid that became turbid after several hours of mixing. The hexagonal nanoflakes in the order of 50 nm and composed of 2–3 nm nanograins (mosaic structure) with an approximate 10 nm thickness (Fig. 4.4A and B) were obtained (Oaki and Imai, 2007). The preparation of metal oxide nanomaterials by biomimetic process happens at relatively lower temperature and minimizes the particle degradation compared to the conventional techniques.

4.3 PROCESSING OF METAL OXIDE-BASED POLYMER NANOCOMPOSITES The symbiotic properties of the metal oxide nanoparticle-polymer nanocomposites have attracted the interest of researchers. The hybrid nanocomposites demonstrate a high elastic stiffness, wear resistance, enhanced thermal, and conductive properties. The volume



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Fig. 4.4 Overview of manganese oxide and cobalt hydroxide nanoflakes. (A and B) Manganese oxide with (A) FETEM image and Tyndall light scattering inset and (B) HAADF-STEM image of magnified flakes. (C and D) Cobalt hydroxide nanoflakes with (C) FETEM image and dispersed inset and (D) HAADF-STEM of mosaic structure. (Reprinted from Oaki, Y., Imai, H., 2007. Biomimetic morphological design for manganese oxide and cobalt hydroxide nanoflakes with a mosaic interior. J. Mater. Chem. 17, 316–321 with permission of Royal Society of Chemistry.)

fraction of the components, including the interfacial interactions between the matrices and nanomaterials are the key parameters for achieving the effective properties of the nanocomposites. Due to their agglomeration behavior, effective dispersion of nanoparticles in polymer matrix is always a challenging task (Sanchez et al., 2001; Schadler, 2003). There are three common techniques for the preparation of polymer/metal oxide nanocomposites (Fig. 4.5). The first method is the in situ polymerization of monomers in the presence of metal oxide nanoparticles. The second is the direct mixing/blending of metal oxide nanoparticles and polymer via melt or solution mixing. The third is the solgel process. The in situ synthesis process involves the dispersion of metal oxide nanoparticles in a monomer and the subsequent polymerization of the monomer. Highly dispersed γ-Fe2O3 nanoparticles in a crosslinked polystyrene resin were prepared in a single-step

Metal Oxide Based Nanomaterials and Their Polymer Nanocomposites

In situ polymerization Metal oxides



Sol-gel process

Sol-gel process Polymer

Metal oxide precursor

Fig. 4.5 Preparation of metal oxide nanoparticles/polymer based nanocomposites.

process (Ziolo et al., 1992). The authors used an aqueous solution of Fe(II)/Fe(III)chloride and synthetic resin for the ion exchange. ZnO and TiO2 based PMMA nanocomposites were prepared using an in situ bulk polymerization process (Demir et al., 2007), where alkylphosponic acid was used for modifying the surface of nanoparticles. Polybutylene succinimide diethyl triamine modified hydrophobic TiO2 nanoparticles were synthesized and dispersed 5 wt% of these particles in styrene prior to the miniemulsion process (a type of in situ polymerization technique) (Erdem et al., 2000). Approximately 89 wt% of nanoparticles was encapsulated in polystyrene. This technique has also been used to synthesize PS/TiO2 nanocomposite spheres using with both an organic monomer and an inorganic precursor trapped in the miniemulsion droplets (Wu et al., 2010) (Fig. 4.6). Firstly the oil/water (O/W) miniemulsion, made with oil composed of acetylacetone chelated tetra-n-butyl titanate (TBT), and styrene was prepared, in which the oil droplets were stabilized by a cationic surfactant, CTAB and costabilizer, hexadecane. The polymerization of styrene and the sol-gel reaction of TBT occurred inside the miniemulsion droplets, causing formation of PS/TiO2 nanocomposite spheres. The hydrophilic TBT diffused to the O/W interface during the polymerization of styrene, and TiO2 nanoparticles formed by the hydrolysis and condensation of TBT were adsorbed successfully onto the surfaces of the polymer through electrostatic interactions. The sol-gel approach has been implemented to improve compatibility at the molecular level between inorganic and organic components. The process consists of two main reactions; condensation and hydrolysis. Hydrolysis involves the cleavage of the organic chain bonding to metal and subsequent replacement with –OH groups through nucleophilic addition, whereas condensation is based on –O–M–O– bond formation (Hench and West, 1990). The solvent, amount of water, temperature, and metal reactivity are the main parameters. Compared to conventional reactions, materials prepared by sol-gel processing have uniformity, low sintering temperature, and high purity. The process has



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Fig. 4.6 Formation of PS/TiO2 nanocomposites in a single step (see text for details). (Reprinted with permission from Wu, Y., Zhang, Y., Xu, J., Chen, M., Wu, L., 2010. One-step preparation of PS/TiO2 nanocomposite particles via miniemulsion polymerization. J. Colloid Interface Sci. 343, 18–24 copyright Elsevier.)

been used to prepare the TiO2/polymer nanocomposites with covalent linkages by the in situ sol-gel process (L€ u and Yang, 2009) (Fig. 4.7). Blending, the ex situ method is the simplest method for the preparation of metal oxide/ polymer nanocomposites, and can normally be divided into solution blending and melt blending. Melt blending was performed to prepare the poly(butylene succinate)/TiO2

O Ti O

O Ti

O Ti


O Ti


O O Ti R

Titania nanodomains


O Polymer matrix

End-capped polymers R = -Si(OR)3 or -COOH Organic backbone


Thermal curing


Forming films





Polymers with pending functional groups

Organic-inorganic hybrid nanocomposites

Fig. 4.7 TiO2-polymer nanocomposites via the in situ sol-gel route. (Reprinted with permission from L€ u, C., Yang, B., 2009. High refractive index organic-inorganic nanocomposites: design, synthesis and application. J. Mater. Chem. 19, 2884 with permission of Royal Society of Chemistry.)

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nanocomposites using an extruder as the processing equipment (Miyauchi et al., 2008). The authors have evaluated their photo-induced decomposition and biodegradability in relation to the dispersion state of TiO2 nanoparticles. Compared to melt blending, solution blending is used more widely in laboratory scale for nanocomposites processing; however, due to its low cost and simplicity in large-scale production for commercial applications, melt processing is still the preferred choice for industries.

4.4 PROPERTIES OF METAL OXIDE-BASED POLYMER NANOCOMPOSITES Owing to their unique properties, metal oxide nanomaterials plays an important role in a wide range of applications, including catalysis, magnetic resonance imaging (MRI), tissue engineering, cancer treatment, paints, waste water treatment, etc. Table 4.1 summaries the properties and applications of selective metal oxide nanoparticles.

4.4.1 Physical, Rheological, and Mechanical The addition of nanomaterials into polymer matrix enhances the stiffness, and strength via reinforcement mechanisms. Moreover, several characteristics vary due to the size and shape of the nanoparticles such as Young’s modulus, shear modulus, coefficient of thermal expansion, electrical and thermal conductivity. Due to an increase in the surface energy of nanoparticles they changes the crystallographic structure, (Dasari and Njuguna, 2016) and thus affects the reactivity including the electrical and optical properties for the prepared nanocomposites. In order to understand the viscoelastic flow behavior of the system, rheological characterization of polymeric nanocomposites is very important, as it gives an overall idea about how the addition of various fillers influences the structure-property relationship. The addition of nanofillers usually led to a dramatic decrease in the viscosity values of the neat polymer due to the uniform dispersion of nanoparticles in a polymer matrix which reduces the tendency toward uncontrolled flocculation. At a low loading of fillers the polymer filler composite systems usually behaves like Newtonian fluid; at a higher loading, there is a tendency to change from Newtonian to non-Newtonian behavior (Mohan et al., 2016). Maharramov et al. (2018) has investigated the structural and dielectric properties of isotactic polypropylene and iron oxide nanoparticle-based polymer nanocomposites. The SEM studies revealed the homogeneous distribution of these iron oxide nanoparticles in the polymer matrix, at different percentages of loading of iron oxide nanoparticles, as shown in Fig. 4.8. From the SEM, it was identified that the iron oxide nanoparticles ranging from the 15–18 nm for 5 wt% loading of iron oxide and 16–20 nm for 7 wt% loading. The supramolecular structure of polymer also changes with the increase in the concentration of iron oxide nanoparticles and forms the ordered structure. The dielectric permittivity measured by the impedance spectrometer observed that



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Table 4.1 Metal oxide nanoparticles and their applications and properties Nanomaterial Applications Properties References




Magnetic oxide

Photocatalytic degradation of organic pollutants, dye-sensitized solar cells, gas sensor, nanomedicine, skin care products, and antimicrobial applications Thermal conductivity, antioxidant, antibacterial, antimicrobial, catalytic, battery solar cells, and gas sensor

Catalytic, anticorrosion, optical, electronic, spectral, structural, mechanical and sensing properties

(Parala et al., 2002; Teleki et al., 2006; Chen and Mao, 2007; Ho et al., 2007; Mizukoshi et al., 2007; Zhang et al., 2009)

Photoconducting, sensing, thermal, electrical, optical, magnetic, and dielectric, properties

Photocatalytic degradation of organic pollutants, optoelectronic and electronic device applications, medical filling materials gas sensor, cosmetics, and antimicrobial applications MRI, drug delivery, biomedicine, cancer treatment, removal of toxic metal ions, and antimicrobial

Magnetic electronic, catalytic, thermal conductivity, optical, electrical, sensing and transport

(Borgohain et al., 2000; Vijaya Kumar et al., 2000; Poizot et al., 2003; Kida et al., 2007; Yuan et al., 2007; Son et al., 2009a; Saito et al., 2011; El-Trass et al., 2012) (Kahn et al., 2005; Padmavathy and Vijayaraghavan, 2008; Bo jesen ̸ et al., 2012)

Physical, sensing, magnetic, caloric, and hydrodynamic properties

(Jolivet et al., 2004; Alexiou et al., 2006; Chertok et al., 2008; Park et al., 2012)

the dielectric constant was increased relative to the concentration of nanoparticles and the value of ε; dielectric permittivity does not change with the increase in frequency and changes with the increase in temperature, as shown in Fig. 4.9. The ion conductivity is directly associated with the temperature; until the 318 K, there is a decrease in the conductivity and started increasing from the 358 K due to the destruction of polymer crystalline phase, hence the distance increases between the nanoparticles. Fluorescent epoxy nanocomposites reinforced with polydopamine (PDA)functionalized zinc oxide (ZnO) nanoparticles have been discussed by Liang and

Metal Oxide Based Nanomaterials and Their Polymer Nanocomposites

Fig. 4.8 SEM of polymer nanocomposites of polypropylene and iron oxide particles (A) 5% iron oxide and (B) 7% iron oxide nanoparticles. (Reprinted from Maharramov, A.A., Ramazanov, M.A., Di Palma, L., Shirinova, H.A., Hajiyeva, F.V., 2018. Influence of magnetite nanoparticles on the dielectric properties of metal oxide/polymer nanocomposites based on polypropylene. Russ. Phys. J. 60, 100–104 with permission of Springer.)

Fig. 4.9 (A) dielectric permittivity dependence on frequency with different concentration of iron oxide (1) 1%, (2) 3%, (3) 5%, (4) 7%, and (5) 10%. (B) Dielectric permittivity temperature dependency of nanocomposites. (Reprinted from Maharramov, A.A., Ramazanov, M.A., Di Palma, L., Shirinova, H.A., Hajiyeva, F.V., 2018. Influence of magnetite nanoparticles on the dielectric properties of metal oxide/ polymer nanocomposites based on polypropylene. Russ. Phys. J. 60, 100–104 with permission of Springer.)

coworkers (Liang et al., 2017), where results reveal that the PDA functionalized ZnO nanoparticles were dispersed uniformly in the epoxy matrix. The results of the tensile strength values showed that compared to pure epoxy (83.8 MPa) as well as epoxy loaded with ZnO nanoparticles (91.5 MPa), an enhanced in tensile strength of the epoxy nanocomposites filled with PDA functionalized ZnO nanoparticles (up to 106.7MPa) was obtained. The Tg results demonstrate that compared with that of pure epoxy (118.3°C), Tg of epoxy nanocomposites filled with PDA functionalized ZnO nanoparticles has shifted to a higher temperature (127.0–132.0°C).



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Multiwalled carbon nanotubes (CNT), thermally reduced graphite oxide (TrGO), and spherical metal nanoparticles (CuO) based ethylene-1-butene thermoplastic elastomeric copolymers were prepared via the melt mixing method. The effect of nanomaterials on the elastic modulus of the pure elastomeric polymers was studied, where a 3–4 times increase in the elastic modulus of the stiffer matrix was achieved compared to the pristine matrix; however, TrGO nanoparticles rendered even larger improvements with nanocomposites based on the softer matrix reaching values as high as seven times the modulus of the pristine sample at concentrations less than 10 vol%. Spherical metal oxide nanoparticles otherwise rendered outstanding improvements in the elastic modulus (around 60%) at concentrations as low as 2 vol% (Palza et al., 2016).

4.4.2 Thermal and Chemical The extraordinary properties make metal oxide nanomaterials excellent candidates for the development of polymer nanocomposites with higher thermal and chemical stability. Solid epoxy resin, DGEBA/biguanidine matrix, and metal oxides based nanocomposites were prepared by means of a twin-screw extruder, where two different nanoparticles based on alumina and zinc oxide at the composition of 3 wt% were incorporated. The results show that the activation energy of the curing reaction was 65 kJ/mol, whereas after adding ZnO, a minimum of 53 kJ/mol was reached. The lower activation energy of this nanocomposite allows for the maximum reaction and consequently an enhanced crosslinking network. Thus the glass transition temperature is increased from 368 K in the pristine polymer to 377 K after reinforcement. The nanocomposite filled with alumina has a corresponding activation energy of 61 kJ/mol; this might be due to short chain segments, which could possess higher reticulation near the surface particles (Karasinski et al., 2013). Simendic and colleagues have prepared a series of thermoplastic polycarbonate-based polyurethane (PC-PU) nanocomposites by the addition of ZnO nanoparticles (0.5, 1, and 2 wt%). Thermal stability and other thermal properties of the obtained nanocomposites were studied by thermogravimetry (TGA) and differential scanning calorimetry (DSC) analyses, where it was found that the addition of ZnO particles may cause the disruption of phase separation, and hence affect thermal and mechanical behavior of segmented polycarbonate-based polyurethane nanocomposites (Pavlicˇevic et al., 2014). Thermally stabilized metal-organic chromophores have been generated through an electrochemical oxidation of zinc metal to form a ZnO-chromophore nanomaterial. The chromophores are surface bound to ZnO by a polar covalent metal-to-chromophore bridge which minimizes thermal degradation pathways of the organic molecules. The prepared nanocomposite demonstrates a thermal stability up to 300°C. A dramatic increase in photostability compared to the pure chromophore or the metal-chromophore nanomaterial was observed for the nanocomposites (Skorenko et al., 2016).

Metal Oxide Based Nanomaterials and Their Polymer Nanocomposites

A new class of transparent epoxy-based nanocomposite coatings containing starchmodified nano-zinc oxide (ZnO-St) was also discussed, where ZnO nanoparticles physically decorated with starch carbohydrate polymer increased compatibility with epoxy chains and sterically prevented flocculation of ZnO nanoparticles. Curing behaviors of epoxy and transparent nanocomposites containing ZnO and ZnO-St were also studied. The ZnO-St, particularly at a low heating rate of 5°C/min, prolonged the curing process (corresponding to ΔT increase of ca. 166 for epoxy to 200°C for Zn-St/epoxy), and increased the amount of heat release (in the same order from 328 to 380 J/g) due to the epoxide ring opening by starch hydroxyl groups. Such nanocomposite based coatings can be applied as top coats owing to their transparency (GanjaeeSari et al., 2018).

4.4.3 Electrical and Optical Metal oxide nanoparticles shows special optical and electronic properties as compared to those of bulk materials. The metal oxide-based polymer nanocomposites also exhibit good electrical and optical properties and thus have long been of interest for researchers. The optical materials are very hard to originate from a single crystal; they require environmental protection that is easy to mold in the nanocomposites. The optical materials exhibit enhanced properties at a nanoscale level, and the polymer matrix is used to hold the nanoparticles together. The electrical properties of polymer nanocomposites differ when the nanoparticles are in nano scale for many reasons. Initially due to the quantum effects, decrease in size of the particle decreases the interparticles spacing for same volume of fraction, thus percolation occurs and increases the electrical properties. Compared to microfillers the addition of ZnO nanoparticles is more impactful to reduce the resistivity (Fig. 4.10), which might be due to the high interfacial resistance and large interfacial area (Parala et al., 2002). The permittivity of the polymers increases with the addition of metal oxide nanoparticles. ZnO, with low-density polyethylene as a polymer, indicated by the addition of 50 wt% of filler exhibited 10% higher in breakdown strength compared to ZnO of microsize particles in low-density polyethylene. In general, organic polymers are used in photovoltaic devices, which are easy and efficient to fabricate, but there is still a need to make improvements in durability and efficiency. Huynh et al. (2003) reported the power conversion efficiency of 1.7% with the incorporation cadmium-selenium in poly(3-hexylthiophene). ZnO-poly(3-hexylthiophene) showed the power efficiency of 0.53%, which is better than the bilayer structure of known components. ZnO nanoparticles were synthesized in the pores that are formed inside the PNIPAm (poly(N-isopropyl acrylamide)) gels during polymerization, where depending on the internal porosity of the gel, the size and distribution of ZnO nanoparticles were changed accordingly. The fluorescence spectra of ZnO nanoparticles released from PNIPAm gel


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1´1020 Resistivity (Ω cm)


1´1018 1´1016 1´1014 1´1012 1´1010

PE/ZnO nanoparticles PE/ZnO micron particles 0


20 30 ZnO content (vol.%)


Fig. 4.10 Resistivity versus volume fraction of ZnO particles. (Reprinted from Hong, J.I., Schadler, L.S., Siegel, R.W., Mårtensson, E., 2003. Rescaled electrical properties of ZnO/low density polyethylene nanocomposites. Appl. Phys. Lett. 82, 1956, doi: with permission of AIP Publishing.)

with low crosslinker concentration have only UV emission, while the nanoparticles released from PNIPAm gel with high crosslinker concentration have both the UV and the green emissions of ZnO (Celebioglu and Yilmaz, 2017). The optical clarity for nanocomposites was quite difficulty to obtain due to the presence of particles, which scatters the light.

4.4.4 Biological Metal oxide nanomaterial-based polymeric nanocomposites exhibit great potential in certain fields of life sciences such as biomedicine, agriculture, and environment. Iron oxide nanoparticles are useful in molecular imaging; these particles are evaluated in vitro and as well as in animal experiments. A cellular magnetic-linked immunosorbent assay was prepared by modifying the enzyme-linked immunosorbent assay as an MRI application for clinical diagnosis (Burtea et al., 2005). Bulte (2006) used iron oxide nanoparticles in the MRI to know the location and migration of cell culture after the transfusion or transplantation. It performed by relabeling of iron oxide magnetic particles and thus opens opportunities to incorporate the labeling magnetic particles in the field of biology and medicine. Biotin and bipyridinium carboxylic acid-coated metal oxide nanoparticles are used for fluorescein-labeled protein (Fan et al., 2003). Dopamine coated on iron oxide nanoparticles using the interaction between the iron oxide surface and the bidentate functional groups was also found highly useful for fluorescein-labeled protein (Xu et al., 2004). Phospholipids coated on the magnetic particles for the separation of protein is also investigated (Bucak et al., 2003). The particles ranging from the 10–100 nm are good for the prolonged blood circulation times and easily used by intravenous injection. These nanoparticles act as

Metal Oxide Based Nanomaterials and Their Polymer Nanocomposites

carriers for drug delivery for treating the cancer cells, and thus are helpful in reducing the effects of conventional chemotherapy. From the observation the accumulation of nanoparticles at the tumor location is induced by the magnetic field gradient (Gallo et al., 1993; Alexiou et al., 2006).

4.5 APPLICATIONS With a wide range of properties, metal oxide nanomaterials play a key role in the inclusive range of potential applications. The incorporation of metal oxide nanoparticles into polymer matrices leads to a number of applications including energy conversion and storage, photocatalysis, gas and humidity sensing, heterogeneous catalysis, biomedical applications, etc. The metal oxide nanomaterials also have potential applications in different fields including paint pigments, pharmaceuticals, cosmetics, medical diagonotics, catalysis and supports, magnetic and optical devices, batteries and fuel cells, flat panel displays, electronic and magnetic devices, structured materials, biomaterials, protective coatings, etc. More interesting applications of metal oxide-based nanostructural materials are found in optical and electrical or optoelectronic sectors. Many of them are important photocatalysts for various organic transformations and photodegradation reactions. The potential applications of polymer/metal oxide hybrid nanocomposites are given in Table 4.2.

Table 4.2 Potential applications of polymer/metal oxide hybrid nanocomposites Nanocomposites Applications References

Poly(amide-imide)/TiO2 High-density PE/TiO2 Chitosan/TiO2 Poly(butylene succinate)/ TiO2 Chitosan/iron oxide Poly(methyl acrylate)/Fe3O4 PEG/iron oxide Starch/iron oxide PVA/CuO Chitosan/CuO Epoxy/ZnO PMMA/ZnO

Composite membranes for gas separation Bone repair Photocatalyst and antibacterial agent Photocatalyst Heavy metal ion adsorption Waste water purification MRI MRI and drug delivery Nanofluids Photocatalyst and antibacterial agent Light-emitting diodes Memory cells

(Camargo et al., 2009) (Hashimoto et al., 2006) (Haldorai and Shim, 2014) (Miyauchi et al., 2008) (Ngah et al., 2011) (Liu et al., 2012) (Allard-Vannier et al., 2012) (Kim et al., 2003; Wang and Zhang, 2007) (Pandey et al., 2012) (Haldorai and Shim, 2013) (Yang et al., 2008) (Son et al., 2009b)



Nanomaterials and Polymer Nanocomposites

4.6 CONCLUSIONS AND FUTURE TRENDS This chapter focuses on the approaches for the synthesis of metal oxide nanoparticles using different physical and chemical techniques including growth mechanism, structure modulation and production of metal oxides. However, the absolute control over the shape and size distribution of metal oxide nanoparticles remains a challenge. Compared to physical methods, the chemical methods have been found to be more effective for the synthesis of metal oxide nanomaterials. The critical issues that need our consideration involve devising inexpensive, greener ways of manufacturing these oxides and obtaining a greater degree of mastery over the manipulation of the shape of the nanostructured metal oxides. Next generation nanoengineered materials can be developed using a low temperature in vitro biomimetic synthesis approaches. Properties like physical, rheological, conductive, optical, and biological of the metal oxide based nanocomposites need to study in details for their better exploration. A very low metal oxide nanoparticles loading is helpful for making improvements to the functional properties of the polymers. There are several factors affecting the properties of the nanocomposites including the state of the metal oxide nanomaterials dispersion in polymer matrix as well as the generation of the microstructural distribution during nanocomposites processing. The development of application-specific metal oxide nanoparticles would be of particular interest for the researchers; however, biocompatibility, toxicity, and long-term stability of the metal oxide nanoparticles remains the challenge that needs to be addressed.

ACKNOWLEDGMENT This work was supported by the grant from Science and Engineering Research Board (SERB-DST), India (Grant No. ECR/2016/001355).

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