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, c0) that is resealed to obtain a master curve.