Mechanisms which can Accelerate the Growth of Phase Separating Domains Near a Wall

Abstract

AbstractThough the dynamics of bulk phase separation during spinodal decomposition is fairly well understood nowadays, recent experiments have shown that the same process occuring near a wall introduces some surprisingly fast domain growth kinetics. Studies of both polymer mixtures and simple binary fluids at critical composition quenched into the unstable regime reveal the presence of a fast mode associated with domains coarsening at the wall. The scattering data indicates that while the bulk domains grow in time as t1/3, as dictated by usual diffusion driven dynamics, the surface domains coarsen with exponents ranging from about 1.1 to 1.5 depending on the quench depth. We construct a model in which the average size of domains in a binary mixture undergoing spinodal decomposition near a wall can achieve growth exponents much larger than 1/3. The accelerated growth is associated with the domains of the non-wetting phase coarsening anisotropically against a wall coated with the wetting phase.The faster growth evolves from coupling Lifshitz-Slyozov type coarsening for critical volume fractions, modified to include the geometric constraint of growth near a wall, the process of domain coalescence. Included are some predictions for experimental tests of these ideas.