Layered-silicate polymer experimental

The effect of polymer-filler interaction on solvent swelling and dynamic mechanical properties of the sol-gel-derived acrylic rubber (ACM)/silica, epoxi-dized natural rubber (ENR)/silica, and polyvinyl alcohol (PVA)/silica hybrid nanocomposites was described by Bandyopadhyay et al. [27]. Theoretical delineation of the reinforcing mechanism of polymer-layered silicate nanocomposites has been attempted by some authors while studying the micromechanics of the intercalated or exfoliated PNCs [28-31]. Wu et al. [32] verified the modulus reinforcement of rubber/clay nanocomposites using composite theories based on Guth, Halpin-Tsai, and the modified Halpin-Tsai equations. On introduction of a modulus reduction factor (MRF) for the platelet-like fillers, the predicted moduli were found to be closer to the experimental measurements. 

The static and dynamic properties of polymer-layered silicate nanocomposites are discussed, in the context of polymers in confined spaces and polymer brushes. A wide range of experimental techniques as applied to these systems are reviewed, and the salient results from these are compared with a mean field thermodynamic model and non-equilibrium molecular dynamics simulations. 

The formation and equilibrium structure of polymer layered silicate nanocomposites, in particular with organically modified layered silicates, has been shown to be a strong function of the nature of the polymer (polar or apolar), the charge carrying capacity of the layered silicate, as well as the chain length and structure of the cationic surfactant. However, both the polymer/silicate compatibility and hybrid equilibrium structure for these nanocomposites are observed to be independent of polymer molecular weight. The experimental results have been summarized by Vaia et al. and a lattice based mean field theory has been developed to explain these results [26]. 

Rheology of various polymer layered-silicate nanocomposites - intercalated, exfoliated and end-tethered exfoliated (prepared by in-situ polymerization from reactive groups tethered to the silicate surface), have been performed in a conventional melt-state rheometer in both oscillatory and steady shear modes. These experimental studies have provided insight into the relaxation of polymer chains when confined by the layers of inorganic silicates, as well as the role of shear in orienting the layered nanocomposites. 

Experimental results obtained allow to mark a promise of this research direction. Developing new polymer composite materials based on natural layered silicates and polyethyleneterephthalate - the most needed polymer material - gives opportunity to modify PET properties and therefore expand the field of its application. 

On a thermodynamic ground, nanoscale mixing of layered silicates with polymers is only possible if the chemical structure of both components is such to grant favorable energetic interactions [4-8]. However, the morphology of experimental nanocomposites will be dependent on kinetics as well, and, consequently, on the pathway of their preparation. 

Taking into account the discrepancy in theoretical and experimental data for epoxy polymer/Na -montmorillonite nanocomposites, it can be supposed that the interfacial layer thickness for them is smaller than 0.5 d - d j), i.e., the interfacial layer does not fill the entire space between silicate platelets. The value of /. can be estimated according to the following fractal relationship [26] ... 

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