Atomic force microscopy study of environmental responses on poly(vinyl alcohol)-graft-polystyrene surfaces

An environmentally induced surface rearrangement occurring on poly(vinyl al cohol)-graft-polystyrene (PVA-PS) surfaces has been studied by means of an atomic force microscopy technique. In a dry state, the graft copolymer film surfaces were covered by a thin flexible layer of PS component on a PVA su blayer. The topmost PS layer became unstable when the film was immersed in water. A dewetting process took place to generate a "hole-with-rim" pattern for the graft copolymers with 12-23 mol % PS content. The number of the "h ole-with-rim" structure increased along with the immersion time, while thei r sizes were not appreciably varied. The dewetting process for the graft co polymers with 26-41 mol % PS content, on the other hand, produced a "wormli ke" pattern, which corresponds to the microphase separation morphology obse rved in dry state. The graft copolymer film recovered from water and dried at 120 degrees C reproduced the original smooth surface morphology, while f ilm dried at ambient temperature maintained a notably rough surface morphol ogy.