Article pubs.acs.org/Langmuir
Evolution of Homopolymer Thin-Film Instability on SurfaceAnchored Diblock Copolymers Varying in Composition Xiao-Jing Cai,† Jan Genzer,† and Richard J. Spontak*,†,‡ †
Departments of Chemical & Biomolecular Engineering and ‡Materials Science & Engineering, North Carolina State University, Raleigh, North Carolina 27695, United States ABSTRACT: The stability of molecularly thin polymer films deposited on various material substrates is of critical importance to many contemporary nanotechnologies involving functional coatings and nano/micropatterned surfaces, in which case the causes responsible for film destabilization must be fully understood. Previous experimental studies report that factors such as film thickness and polymer molecular weight play significant roles in governing the rate, as well as mechanism, of destabilization. Complementary theoretical predictions reveal that surface heterogeneities can likewise induce (and regulate the process of) destabilization. In this study, we investigate the destabilization rate and mechanism of homopolystyrene (PS) films differing in thickness on top of poly(styrene-b-methyl methacrylate) (SM) diblock copolymer monolayers varying in chemical composition anchored to flat silica-like substrates to examine the effect of surface constitution on PS stability. Copolymers with a long M block consistently promote PS dewetting by nucleation and growth, wherein the linear dewetting rate decreases monotonically with increasing PS molecular weight, film thickness, and S fraction in the SM copolymer. In analogous studies involving a copolymer with a relatively short M block, however, PS dewetting proceeds instead by spinodal dewetting that evolves gradually into nucleation and growth as the film thickness is increased.
■
INTRODUCTION Contiguous, as well as nano/micropatterned, polymer thin films are of significant fundamental interest1−3 and hold tremendous promise for a wide variety of contemporary applications,4−6 promising examples of which include protecting coatings, organoelectronics, and solar cells, just to name a few. If a bulk polymer droplet in contact with a substrate spreads freely and thus exhibits a contact angle of
