Rheology and Anomalous Flow Properties of Poly(ethylene-alt-propylene)–Silica Nanocomposites.

In this work, poly(ethylene-alt-propylene)–silica nanocomposites, constitutinga model nanocomposite system with mostly nonattractive interactions,are studied by means of oscillatory shear rheology. Two differentmolecular weights were used in order to consider both the effect ofnanoparticle presence on the relaxation of short as well as long polymermatrices. An increase of the particle fraction leads on the one handto the observation of typical characteristics of colloidal rheologysuch as mechanical reinforcement and the formation of a particle gel.On the other hand and in the focus of our analysis, the increasingparticle presence also directly affects the relaxation of the polymerchains. In particular, a shift of the polymer loss maximum in G″(ω) is found in the entangled matrices, whereasanomalous flow behavior is evidenced in the rheology data of highlyfilled short matrices. We succeeded to explain these macroscopic observationsfrom the rheology experiments by considering small-angle neutron scatteringand neutron spin echo results on the same samples, which yield detailedinsight into the molecular circumstances responsible for the observedmacroscopic property changes. [ABSTRACT FROM AUTHOR]