Temperature dependence of surface reorganization characteristics of amphiphilic block copolymer in air and in water studied by scanning force microscopy

Abstract

We have investigated the surface reorganization characteristics of a novel amphiphilic diblock copolymer, poly(acetic acid-2-(2-(4-vinyl-phenoxy)-ethoxy)-ethylester)-block-polystyrene (PAEES-b-PS), in response to varying interfaces from air to water and vice-versa at various temperatures. The surface reorganization characteristics of the block copolymer films was monitored by scanning force microscopy, in order to delineate the kinetically controlled morphological process of surface reorganization of a diblock copolymer, with a particular emphasis on the phase contrast signal which allowed the determination of local composition patterns of PAEES-b-PS at the surface. Upon heating a water-annealed sample in air, the initially hydrophilic liquid-like surface exhibited a typical dewetting pattern comprising holes and elevations of different copolymer components. In contrast, air-annealed samples with glassy polystyrene surfaces exhibited a distinctly different reorganization pattern upon heating in water, possibly due to the swelling of the underlying liquid-like hydrophilic block by penetrated water. In both air and water environments, the major surface reorganization occurred around 70℃, well below the glass transition temperature (100℃) of the higher Tg block, polystyrene, in the copolymer.