Nanopartides polymer nanocomposites

In conventional composites, the models of thermal conduction are based on the Fourier heat conduction theory. However, these models are not valid at the nanoscale due to the ballistic phonon transport and interfacial scattering. Chen et al. [31] have reviewed the status and progress of theoretical and experimental studies of thermal transport phenomena in nanostructures. We discuss here some theoretical and numerical efforts toward the prediction of thermal conductivity of nanopartide-polymer nanocomposites. 

DPD simulation has been applied to predict the rheological and viscoelastic behaviors of nanopartide-polymer nanocomposites and to examine the effects of particle shape, particle-particle interaction, and partide dispersion states of such behaviors. It was found that partide-particle interaction has a distinct effect on the dynamic shear modulus. Havet and Isayev [39,40] proposed a rheological model to predict the dependence of dynamic properties of highly interactive filler-polymer mixtures on strain and the dependence of shear stress on shear rate. 

In a novel application of supercritical COj, Charpentier et td. [366] prepared bionanocomposites of PVAc and SiOj nanopartides using a one-pot synthesis in supercritical COj wherein all raw chemicals, tetraethoxysilane (TEOS)/tetramethoxysilane (TMOS), vinyltrimethoxysilane (VTMO), vinyl acetate, initiator, and hydrolysis agent were introduced into one autoclave. They found that PVAc nanocomposites with well-dispersed SiOj nanopartides of 10-50 nm were formed opening new opportunities such as the production of metal-oxide-polymer nanocomposites from liquid precursors. 

It is well knovm that the behavior of polymer chains around the partide surface is different from that of bulk polymer chains. Depending on the nanopartide-polymer interactions, polymer in the vicinity of the nanopartide may be developed into crystallized, amorphized, or heterogeneously nudeated structures. The crystallization of polymer will dramatically affect the overall properties of polymer nanocomposites. As a result, when predicting nanocomposite properties, the morphological features and properties of the interfadal polymer must be taken into account in addition to the properties of individual nanoparticles and bulk polymer. 

In the following sections, we will discuss briefly some analytical and numerical techniques, followed by their apphcations to the property prediction of nanocomposites with a focus on nanopartide-reinforced polymer nanocomposites. 

The direct use of micromechanical models for nanocomposites is however doubtfid due to the significant scale difference between nanoparticles and macro-partides. As such, two methods have recently been proposed for modeling the mechanical behavior of polymer nanocomposites equivalent continuum approach and self-similar approach. In equivalent continuum approach, molecular dynamics (MD) simulation is first used to model the molecular interaction between nanopartide and polymer. Then, a homogeneous equivalent continuum reinforcing element (i.e., an effective nanopartide) is constmcted. Finally, micro-mechanical models are used to determine the effective bulk properties of a... 

Mechanical properties of polymer nanocomposites can be predicted by using analytical models and numerical simulations at a wide range of time- and length scales, for example, from molecular scale (e.g., MD) to microscale (e.g., Halpin-Tsai), to macroscale (e.g., FEM), and their combinations. MD simulations can study the local load transfers, interface properties, or failure modes at the nanoscale. Micromechanical models and continuum models may provide a simple and rapid way to predict the global mechanical properties of nanocomposites and correlate them with the key factors (e.g., particle volume fraction, particle geometry and orientation, and property ratio between particle and matrix). Recently, some of these models have been applied to polymer nanocomposites to predict their thermal-mechanical properties. Young s modulus, and reinforcement efficiency and to examine the effects of the nature of individual nanopartides (e.g., aspect ratio, shape, orientation, clustering, and the modulus ratio of nanopartide to polymer matrix). 

Stiffness is often a critical property of a material that determines how much a component will deform in response to force (e.g., stretching, compression, or bending). Molecular modeling has been used to predict the stiffness and strength of polymer nanocomposites with different types of nanopartides, for example, carbon... 

The addition of fillers into polymer matrix can alter the rheological properties of the polymer and its processing performance. The rheological properties are affected by the nature of nanopartides and polymer (e.g., molecular weight and polarity) and nanoparticle-polymer interactions. Meanwhile, the applications of polymer nanocomposites depend on their viscoelastic properties that determine their processibil-ity and mechanical integrity. Although some theoretical work has recently been done, our understanding of the viscoelastic properties of polymer nanocomposites and the influence of nanopartide-polymer interactions is quite immature. 

Eor example, the effective elastic properties of silica nanopartides-reinforced polymer nanocomposites were predicted by means of various FEM-based computational models [70], induding an interphase layer around partides as a third constituent material in the prediction of the mechanical properties. Boutaleb et al. [30] studied the influence of structural characteristics on the overall behavior of silica spherical nanoparticles-polymer nanocomposites by means of analytical method and FEM. They assumed that the interphase between silica partide and polymer matrix presents a graded modulus, ranging from that of the silica to that of the polymer matrix, for example, a gradual transition from the properties of the silica to the properties of the polymer matrix (Figure 5.6). The change in elastic modulus in the interphase was described by a power law introducing a parameter linked to interfacial features. 

Metal nanopartides can also be cited. The characteristic properties of metal nanopartides and nanocomposites have been the subject of study because of their unique optical properties. Combining metal and polymer together enhances the optical properties of nanometals. Srivastava et al. 3] studied the optical properties of gold nanocomposites by changing the size and fraction of gold nanopartides. The optical properties of nanocomposite films of various thicknesses with different sizes and volume fraction of gold nanopartides have been studied using spectroscopic... 

Vaia, R.A. and Maguire, J.F. (2007) Polymer nanocomposites with prescribed morphology Going beyond nanopartide-filled polymers. Chem. Mater., 19, 2736-2751. 

This chapter is organised as follows Following this introduction as section 1, a brief description of the synthesis and characterisation techniques used for the as-synthesised polymer capped selenide nanopartides is given as section 2. In section 3, the mechanism of the reaction, results and discussion of the different selenide nanocomposites obtained using different polymers are given. Section 4, the last section gives a summary of the whole process, followed by references. Acknowledgements are cited before references. 

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