A frictional molecular model for the viscoelasticity of entangled polymer nanocomposites

Experimental observations indicate substantial differences in the rheology and dynamics of polymer liquids reinforced with colloidal and nanosize particles compared to complex fluids filled with micron sized particles (Reynaud et al. 2001; Zhang and Archer 2002, 2004; Donnet 2003). The filler size effect on the overall material behavior has been attributed to either inter-particle or polymer-particle energetic interactions, both occurring at the nanoscale. The first mechanism originates from the formation of spatial agglomerated structures of small particles (due to electrostatic and van der Waals’ forces) and the evolution of these structures during loading (Leonov 1990; Heinrich and Klüppel 2002; Cassagnau and Mélis 2003). When fillers are well dispersed in the matrix, reducing the filler size while preserving the filler volume fraction leads to a dramatic increase of interfacial area and a reduction of the average wall-to-wall distance between fillers. Under such circumstances, a large fraction of chains are in contact with at least one filler, some of them forming bridges between neighboring particles. Very similar to the rheology of confined polymer thin films (Subbotin et al. 1995), the dynamics of such systems is controlled by the polymer-filler affinity and the stick-slip motion of chains close to the filler surface (Havet and Isayev 2001, 2003). This perturbs the viscoelastic behavior of the entire matrix phase. Such an effect also exists in composites with much larger fillers (e.g. micron size); however, the volume of perturbed matrix is limited to the interfacial boundary layer which represents a negligible fraction of the total volume of the material. Alireza S. Sarvestani Catalin R. Picu A frictional molecular model for the viscoelasticity of entangled polymer nanocomposites