Surface-Influenced Phase Separation in Organic Thin Films on Drying

Kinetics of phase separation at the air/polymer interface in a binary polymer mixture on evaporation of common solvent is studied. The lateral dimension of the highly anisotropic, pancake-like, minority phase increases with a growth exponent of 2 / 3, identical to “late-stage” growth under (classical) thermal quench at interface. The “wetting-layer” formed at the surface is directly visualized using atomic force microscopy. In contrast to the thermal quench, during drying the kinetics depends on the initial condition (i.e., initial concentration, c 0 ) that is resealed to obtain a master curve.