Abstract
A solution rheology method has been applied to resolve component friction dynamics in polymer mixtures. The approach consists of separately evaluating viscoelastic properties of entangled “object” solutions of polymeric A in oligomeric B and “mirror” solutions of polymeric B in oligomeric A. At various compositions, the friction coefficients ζA and ζB associated with both components A and B are obtained by applying the well-established reptation theory to analyze the oscillatory shear measurements of storage and loss moduli of these object and mirror solutions. It is found that ζA(φ,T) and ζB(φ,T) exhibit different temperature and composition dependencies. Specifically, the low-Tg component A, which is low vinylbutadiene (1,4-PB) in the present case, has considerably weaker temperature and composition dependencies in comparison with the high-Tg component B, which is a high vinyl butadiene (1,2-PB). Further analysis indicates the presence of two consecutive glass transitions in the mixtures. A revised free volume theory (FVT) is proposed to assign different levels of free volume to the components in a mixture as the origin of the separable glass transitions.
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