Nanoparticle Clustering and Viscoelastic Properties of Polymer Nanocomposites with Non-Attractive Polymer–Nanoparticle Interactions

Combining X-ray tomography and rheology, we investigate the nanoparticle (NP) clustering and viscoelastic properties of polymer nanocomposites (PNCs) with non-attractive polymer–NP interactions. X-ray tomography reveals linear and compact NP clusters with preferential orientations rather than tenuous NP clustering structures, highlighting the non-equilibrium nature of NP clustering and the influence of processing on morphology of NP clusters. Detailed analyses show that the number density of NP clusters of N NPs follows P(N) ≈ N–k exp(−N/N*) with N* as a constant and k ≈ 1.8 ± 0.2. Moreover, varying the polymer–NP interactions from strongly repulsive to nearly athermal does not alter noticeably the clustering and the percolation behavior of the NP phase. Linear viscoelastic measurements reveal negligible dynamics slowing down and unexpectedly weak mechanical reinforcement of PNCs following the classical Guth–Gold relation, in sharp contrast to the strong NP clustering from structure characterizations. These results point to qualitatively different clustering behaviors and mechanical reinforcement of PNCs with non-attractive polymer–NP interactions from those with strong attractive interactions.