Late-State Ripening Dynamics of a Polymer/Clay Nanocomposite

H Henning Winter, University of Massachusetts - Amherst
X. L. Wang
P. Sun
G Xue

Abstract

A remarkably simple viscoelastic relaxation pattern was found for a physical gel that, beyond its gel point, slowly ripens toward a stable structural state. The material is a nanocomposite that consists of two components, an organoclay and an end-functionalized polymer, which get mixed at prescribed ratio. When freshly combined, the polymer intercalates into the clay galleries and eventually exfoliates the clay. The exfoliation occurs without applying flow. The nanocomposite quickly passes through the gel point and, with increasing ripening time, tr, its characteristic modulus Gc(tr) and relaxation time λc(tr) grow and decay by orders of magnitude, respectively. Surprisingly, their product, Gc(tr)λc(tr), is found to remain constant during the two vastly different structuring processes of intercalation and exfoliation. For the rheological experiments, Gc(tr)λc(tr) = constant means that dynamic mechanical data can be merged into each other by log/log shifting under 45°.