Dynamics of Spinodal Decomposition in Polymer Solutions near a Glass Transition

A model based on the Cahn−Hilliard formalism is used to simulate structure formation in thermally quenched polymer solutions in the vicinity of a glass transition. Simulation results for the system poly(methyl methacrylate)/cyclohexanol are correlated with light scattering and microscopy measurements recently reported in the literature. Good qualitative and quantitative agreement with experimental observations indicates the applicability of current free-volume and thermodynamic theories to quantify the dynamics near a glass transition. The model accurately predicts late-stage scaling exponents, and results show that the early stage of phase separation occurs on time scales ≪ 1 s. Pore growth rates based on zero-free-parameter calculations agree well with experimental observations. Simulations also show that quenching a phase-separated structure below a glass transition can result in the formation of a secondary droplet structure within the polymer-rich phase, prior to freezing-in of the preexisting morphology. Such secondary structures, which have also been observed experimentally, appear to have little or no effect on the calculated structure factor, which is also consistent with light-scattering measurements.