Dewetting of thin film blends containing block copolymer: effects of nonadsorbing block length and substrate Hydrophobicity

The effects of block copolymer adhesion promoters on the dewetting of polystyrene, PS, homopolymer films with degree of polymerization, P, similar to300 are investigated using optical microscopy and atomic force microscopy. The copolymers are poly(deuterated styrene-block-methyl methacrylate), dPS-b-PMMA, having a short anchoring block that is attracted to the substrate and a long nonadsorbing block with a varying degree of polymerization, N-NA. Relative to a homopolymer film on silicon oxide, SiOx, hole growth slows down, and holes stop growing at a diameter of about 100 mum when 1 vol % block copolymer having N-NA < P is added. The hole floor is found to exhibit a roughness of 1.5 nm and a uniform array of irregularly shaped (N-NA similar to 2P/3) and rounder (N-NA similar to P/3) mounds of polymer. In contrast to this partial dewetting, dewetting is entirely suppressed for N-NA > P. Moreover, as the substrate is changed from SiOx to a more hydrophobic and less wettable amino-terminated surface, we observe an improvement in thin film stabilization, and no dewetting is detected. The slowing down of hole growth on SiOx (NNA < P) and the growth suppression on SiOx (NNA > P) and on amine-terminated surface are attributed to the reduction of the interfacial tension between the bulk and the adsorbed chains as the interfacial width between the adsorbed block copolymer and matrix chains increases.