Understanding morphology evolution and roughening in phase-separating thin-film polymer blends

Using forward recoil spectrometry and atomic force microscopy, the entire phase evolution is revealed for a critical thin-film blend deposited on a substrate undergoing symmetric wetting and phase separation. The three main stages are characterized by a trilayer structure, interphase coarsening, and surface roughening. Capillary fluctuations are shown to cause spontaneous rupturing of the interphase resulting in an interconnected network, which eventually forms encapsulated droplets. The surface roughness grows rapidly at first, remains relatively constant (ca. 12 nm), and then increases rapidly to a final macroscopic value of 245 nm, about half the original film thickness.