The Role of Polymer-particle Interactions on the Viscoelastic Properties of Polymer Nanocomposites
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1056-HH08-29
The Role of Polymer-particle Interactions on the Viscoelastic Properties of Polymer Nanocomposites Alireza Sarvestani, and Esmaiel Jabbari Department of Chemical Engineering, University of South Carolina, 301 South Main St., Columbia, SC, 29208 ABSTRACT A molecular model is proposed for the dynamics of polymer chains in dilute polymer solutions containing well-dispersed spherical particles. In the presence of short range energetic affinity between the monomers and filler surface, the equilibrium structure of the adsorbed polymer layer is determined by a scaling theory. The viscoelastic response of the suspension is studied by a Maxwell model. It is shown that the solid-like properties of polymer nanocomposites in low frequency regimes could be attributed to the slowdown of the relaxation process of polymer chains. This process is controlled by the monomer-particle frictional interactions, density of the adsorbed polymer chains on the particles surface (controlled by monomer-particle adsorption energy), and volume fraction of the interfacial layer which can be enhanced by reduction of filler size or increasing the filler concentration. INTRODUCTION Reduction of the filler size to the nanometer scale can lead to substantial changes in the rheology of filled polymer liquids compared to those reinforced with micron sized particles [13]. In particular, polymer composites reinforced with sub-micron fillers, often referred to as polymer nanocomposites, exhibit a significant enhancement in viscoelastic properties compared to microcomposites, at similar filler volume fractions. In frequency sweep tests, this dramatic increase in viscoelasticity is manifested at very dilute concentration of filler particles and by the appearance of a secondary plateau for the viscoelastic moduli at low frequency regimes [4-6]. In this work, we propose a molecular model to predict the viscoelastic response of nonagglomerated spherical particles in the solution of short non-entangled polymers. In particular, the influence of particle size on the frequency response of filled polymer solutions, in the presence of attractive energetic interaction between the particles and polymer matrix is investigated. The model is developed based on de Gennes’ theory of reversible adsorption from dilute solutions [7]. We use the predictions of the reversible adsorption theory to study the equilibrium configuration of the polymer layer on the surface of filler particles. The dynamics of the adsorbed chains and, consequently, the flow characteristics of the suspension are predicted using a Maxwell type kinetic model. A parametric study is performed to examine the extent to which the proposed model can predict the solid-like behavior of polymer nanocomposites at low frequency regimes. MODEL Filler-Polymer Solution Interfacial Structure. Consider an ensemble of non-entangled monodisperse polymer molecules and a random distribution of monodisperse non-aggregated rigid spherical particles. The schematic equilibrium configuration of an adsorbed chain on t
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