Solvo-selective imprinting of a thin polymer blend film for creating multi-length scale patterns

Controlling and spatial ordering of the phase separation in ultra-thin polymer-blend films is a viable approach to create complex surface structures with unique properties. This study reports a facile solvo-selective patterning technique in a phase-separated polymer blend thin film comprising of immiscible polymers polystyrene (PS) and poly(methyl methacrylate) (PMMA). The pattern replication was achieved using capillary force lithography by imprinting the blend films with cross-linked polydimethylsiloxane stamp with grating patterns. The replication was done in the presence of 1-chloropentane or acetic acid vapours, which are selective solvents for PS and PMMA, respectively. This engendered capillary flow of only one phase while the domains of the second phase remain rigid. Depending on the initial as-cast morphology of the film which is a function of the relative proportion of PS and PMMA, a variety of structures were obtained by combining the phase-separated domains with the structure imposed by the stamp. This method can be considered as a simple, one-step technique for creating hierarchical patterns that are likely to find applications in modulating properties of soft surfaces.