Investigating the Molecular Origins of Responsiveness in Functional Silicone Elastomer Networks

Abstract

Dielectric, calorimetric, and dynamic mechanical measurements were performed to delineate the types and dynamic rates of molecular scale motion in modified poly(vinylmethyl siloxane) (PVMS) stimuli-responsive networks, where pendent groups of the form -S-(CH2)n-OH were chemically attached to the vinyl moiety of PVMS. The glass transition temperature (Tg) for the unsubstituted PVMS network matches that previously reported for linear PVMS indicating that the flexibility of the polymer chains is unaffected by the network cross-linking. In contrast, Tg increases with the introduction of pendent groups of the type -S-(CH2)n-CH3 or -S-(CH2)n-OH, where n is 2, 6, or 11, as the different groups constrain the siloxane backbone to differing degrees. The macroscopic response time and amplitude, as previously measured bydynamic contactangle,arecorrelated withtheobservedglass transition temperatures. Onecon- clusion is that the flexibility of the network and the interactions between pendent groups affect responsiveness.