The combined effect of matrix molecular weight, filler concentration, and filler-matrix interactions on the dynamic viscoelasticity of polydimethylsiloxane/clay composites

Abstract

The macroscopic properties of particle-filled polymer melts depend sensitively on the state of particle dispersion and the structure and dynamics of the interfacial polymer layer, which, in turn, are governed by factors like polymer molecular weight (M_w), particle concentration (C), and particle-polymer interfacial interactions. However, the combined effect of these factors on the macroscopic properties is far from fully understood, especially for polymers filled with anisotropic particles. In this work, we investigate the combined effect of M_w, C, and polymer end-group (methyl, Me or hydroxyl, OH) on the dynamic viscoelastic behavior of polydimethylsiloxane (PDMS)/clay composites. The linear viscoelastic behavior of these composites follows a non-monotonic dependence on M_w, which varies considerably with a modification in C or the polymer end-group. Furthermore, for both Me-PDMS/clay and OH-PDMS/clay composites, the non-linear tests reveal either strain softening-hardening-softening or sustained softening beyond the linear regime, depending on the combination of C and M_w. The critical strains for the onset of softening and hardening vary differently with M_w for different combinations of C and the polymer end-group. Our results suggest that the morphology and rheological behavior of these composites are dictated by a complex interplay of various competing effects, namely, particle agglomeration, interfacial polymer packing and density, entanglements, and bridging interactions. These findings give insight into tailoring the properties of polymer composites by adjusting the combination of C, M_w, and particle-polymer interactions.

Graphical abstract