Pattern formation in a thin random copolymer film: Evolution of an intermediate morphology

Previous studies of structural instabilities in thin, nonwetting, liquid ho mopolymer films on substrates have focused on systems that dewet, forming p atterns that reflect fluctuations in the local film thickness. These patter ns range from discrete cylindrical holes throughout the surface of the film to bicontinuous "spinodallike" patterns. In this paper we show that a thin liquid film, a random copolymer, styrene-ran-acrylonitrile (SAN) comprised of 75% styrene and 25% acrylonitrile, of thickness h=12 nm becomes unstabl e and dewets silicon substrates, forming what we describe here as an interm ediate morphology. During the early stage of dewetting, discrete noncylindr ical, irregular, shaped holes appear spontaneously in the film. The number of holes, N, initially increase with time and the morphology of the late st age of growth, after 18 days, is characterized by a bicontinuous pattern, d istinct from conventional spinodal dewetting patterns. The dynamics of patt ern evolution of this intermediate morphology are discussed. (C) 2000 Ameri can Institute of Physics. [S0021-9606(00)70101-2].