Nanocomposites filler geometries

Once the nanotubes have been characterised and polymer/ nanotubes elaborated, their microstructures have to be precisely determined to understand the relations between the process and the nanocomposites macroscopic properties. It is expected that the microstructural parameters that will play major roles (in addition to the filler geometry) are the nanotube dispersion and orientation... 

Abstract This chapter deals with the non-linear viscoelastic behaviour of rubber-rubber blend composites and nanocomposites with fillers of different particle size. The dynamic viscoelastic behaviour of the composites has been discussed with reference to the filler geometry, distribution, size and loading. The filler characteristics such as particle size, geometry, specific surface area and the surface structural features are found to be the key parameters influencing the Payne effect. Non-Unear decrease of storage modulus with increasing strain has been observed for the unfilled vulcanizates. The addition of spherical or near-spherical filler particles always increase the level of both the linear and the non-linear viscoelastic properties. However, the addition of high-aspect-ratio, fiber-like fillers increase the elasticity as well as the viscosity. 

Fig. 68 Comparison of temperature-dependent intensity of first-order Bragg peak for bare matrix copolymer (A) containing 0.5 wt% nanocomposites with plate-like (V), spherical (o) and rod-like ( ) geometry. Data are vertically shifted for clarity. Inset dependence of ODT temperature on dimensionality of fillers (spherical 0, rod-like 1, plate-like 2). Vertical bars width of phase transition region. Pure block copolymer is denoted matrix . From [215]. Copyright 2003 American Chemical Society...

Polymer nanocomposites are combinations of polymers containing inorganic or organic fillers of definite geometries (fibres, flakes, spheres, particulates and so on). The use of fillers, which have one dimension on the nanometre scale, enables the production of polymer nanocomposites. Functional nanocomposites with specific properties can be custom-made by combining metal nanoparticles (MNP) into the polymer matrix. 

Fig. 4 Early work in inorganic nanoclay-polymer composites helped define terminology that has persisted in the field. This scheme demonstrates the differences between phase separated, intercalated, and exfoliated nanocomposites, noticeably when the filler exists in thin platelet or rod geometries. Reprinted from Alexandre and Dubois [46], Copyright 2000, with permission from...

Compared to microcomposites, where the mechanical behavior is mainly a function of the characteristics of filler and matrix and their respective concentrations, generally speaking, two major characteristics define the mechanical performance of polymer nanocomposites (8) the nanoscale size and geometry of the fillers (aspect ratio) and their dispersion into the polymer matrix, and the interaction between the polymer chains and said nanofillers (interphase). This section highlights the influence of these two factors on the mechanical behavior of polymer nanocomposites. 

The most common nanofUlers are inorganic oxides and carbon based nanofUlers with different geometries. We will concentrate on the Si02 nanoparticle and multiwall carbon nanotube (CNT) here. Both types of fillers exhibit rather poor compatibility with the hydrophobic LCER, so they have to be chemically modified with appropriate chemical functionality for LCER. The chemical functimiality on the nanofiller can bond with the resin either by van der Waal forces or chemical bonds. The former is called heterogeneous nanocomposite and the latter is called homogeneous nanocomposite. 

In the past decade, nanoscale particles with excellent electrical properties and anisotropic dimensions, such as carbon nanotubes and metallic nanowires, have sparked considerable interest in the field of polymer composites. The high conductivity and unique geometry of these nanoparticles can increase the electrical conductivity of typical engineering polymers by S cm at very low filler concentrations (< 1 vol.%). Realizing the full commercial potential of these novel materials hinges upon our ability to produce composites with well-defined and controllable properties. This, in turn, requires an in-depth understanding of the stmcture-property relations for the electrical properties of polymer nanocomposites. 

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