Application of Reptation Models to Modeling of the Rheological Behavior of Polymer Nanocomposites

摘要

Characteristic rheological behaviors of polymer nanocomposites have been studied in shear flow and uniaxial elongational flow. Solid-like plateau storage modulus, strong shear thinning at low frequency regions, and strain hardening at elongational flow were observed. Especially, strain hardening is clearly observed for polymers without long chain branches if nanoparticles are homogeneously dispersed in the polymer matrix and interactions between nanoparticles and surrounding polymer molecules are sufficiently strong. Reptation models are used to model the nanoscale dynamics of nanoparticles and macromolecular chains, and the characteristic rheological behavior of nanocomposites can be explained. Brownian dynamics simulation of Doi-Edwards reptation model is applied and two particle constraint coefficients are introduced to express the influence of nanoparticles on molecular orientation and reptational diffusion of polymer chains. In the simulation, stress tensor including link tension coefficient which characterizes anisotropic friction coefficient of the molecular chain is used to obtain material functions by assuming that the anisotropy of friction is altered by the presence of nanoparticles. Additional frictional force between polymer chains and nanoparticles is considered and the suitable relaxation process and chain stretch are incorporated by considering the full chain geometry of polymer molecular chains. All the reptation models considering the effect of nanoparticles are verified by comparing the theoretical results with experimental data for polymer nanocomposites in shear and elongational flows.