Kinetics of phase separation in the presence of slowly relaxing structural variables

Abstract

The linearized Cahn–Hilliard theory of spinodal decomposition of binary mixtures is generalized to the case where there is a coupling to a slowly relaxing variable (e.g., phase separation of polymer mixtures near a glass transition, etc.). A very simplified model calculation is presented which shows that even in the very early stages pronounced deviations may occur from the simple exponential growth predicted by the standard linear theory. Also the growth rate of the unstable fluctuations is strongly affected: A regime is identified where the initial growth rate is independent of wave number k and controlled by the relaxation rate of the structural variable, rather than given by the standard ‘‘uphill diffusion’’ with diffusivity linearly decreasing with k2. Possible applications of these ideas to real systems are briefly discussed.