Shear-induced breakdown and agglomeration in nanoparticles filled polymer: The shift of phase boundary and kinetics

For the nanoparticle-filled polymers, weak attractive interactions between nanoparticles lead to agglomeration and even formation of a network of nanoparticles in the polymer matrix. Both the agglomeration and the deagglomeration (breakdown) of the particle network are affected by the shear flow, resulting in shear-induced liquid-solid (L-S) transition and shear-induced solid-liquid (S-L) transition, respectively. In this study, we quantify the percolation threshold of both transitions under shear-induced agglomeration and shear-induced breakdown processes. Both the present shear condition and the preshear condition affect the percolation threshold, which turns to only shear rate dependence under steady shear condition, indicating no shear hysteresis. A scaling relation is suggested to describe the percolation threshold at low shear rate. The critical strains at both S-L and L-S transitions are inversely proportional to the distance of the particle concentration to the percolation concentration under steady shear. The apparent phase boundary under shear, represented by the shear rate and shear history-dependent percolation threshold, is further conceptually converted to the space of structural parameter, from which the possible transitions pathway under steady shear are discussed.