Spinodal Decomposition of a Symmetric Critical Mixture of Deuterated and Protonated Polymer.

A nearly symmetric critical mixture (phi sub c = 0.486) of perdeuterated and protonated 1,4-polybutadiene exhibiting an upper critical solution temperature T sub c = 61.5 += 1.5C has been quenched from the homogeneous state (~= 75C) to various temperatures between 25 and 57.5C. Light scattering measurements document the subsequent spinodal decomposition process which we describe based on a four-stage model: early, intermediate, transition, and final. The early stage is accounted for by Cahn theory, yielding initial correlation lengths and effective diffusion coefficients in quantitative agreement with mean- field predictions. Nonlinear effects mark the beginning of the intermediate stage, which exhibits a simple powerlaw growth of heterogeneity length L sub m (t) ~ t sup n sub (eff) , but with a temperature dependent exponent n sup (eff).