Component terminal dynamics in weakly and strongly interacting blends.

Abstract

Miscible blend dynamics have been long been a subject of interest and are not as well understood as dynamics of homopolymer melts. Their anomalous behavior, such as time-temperature superposition failure, broadening of calorimetric glass transition, etc., makes these systems very intriguing and challenges our understanding of miscible blend dynamics. In this work we investigated temperature and composition dependence of two different, dynamically heterogeneous blend systems using rheology and forced Rayleigh scattering (FRS). The first blend investigated was a weakly interacting one comprising poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA). Monomeric friction factors of PEO and PMMA were reported for a wide range of temperature and composition. PEO terminal dynamics were found to have strong composition dependence unlike that of PEO segmental dynamics previously reported. Also, PEO maintained its rapid relaxation mechanisms even in stiffer surroundings. The PEO hydroxyl end groups were found to have no significant impact on component chain dynamics. The FRS and rheology results agreed remarkably well for this system. The Lodge-McLeish model failed to describe the experimental results. In order to understand the role of hydrogen bonding on chain dynamics, a strongly interacting system of PEO/poly(vinyl phenol) (PVPh) was investigated using rheology. The blends consisted of a high molecular polymer tracer dispersed in low molecular weight matrix to extract relevant dynamic information from tracer contribution to material properties. Monomeric friction factors were reported for a wide temperature and composition range. Time-temperature superposition failure was observed in PEO tracer blends at high PVPh concentration. The shape of tracer relaxation spectra for PVPh tracer blends had a strong composition dependence while those for PEO tracer blends were independent of composition. The tracer contribution to blend viscosity had a strong temperature dependence at high PVPh composition. Across the composition range, single and narrow glass transitions were observed for these blends. PVPh chain conformations were investigated using SANS and contradictory conclusions were reached. Therefore, no conclusive remarks can be made regarding PVPh chain conformations in dilute solution.