Surface Wrinkling on Polymer Films.

A series of gold precursor solutions are prepared by dissolving HAuCl4 and its mixtures with K2CO3 of different contents in deionized (DI) water. Neat HAuCl4 predominately forms AuCl4- ions in an aqueous solution. In the presence of K2CO3, AuCl4- ions hydrolyze to form [AuCl4-x(OH)x]- complex ions. Increasing the content of K2CO3 in a gold precursor solution increases the content of [AuCl4-x(OH)x]- complex ions and decreases the content of AuCl4- ions. Poly(4-vinyl pyridine) (P4VP) films of two different molecular weights are deposited on SiOx/Si by spin coating, by which the thicknesses are controlled by polymer weight fractions in butanol. Those P4VP films form periodic wrinkles when immersed in aqueous solutions, followed by drying. The surface wrinkling is induced by swelling pressure that overwhelms the mechanical property of the P4VP film. The periodicity and amplitude of wrinkles grown on the P4VP films strongly correlate with initial thickness, AuCl4- ion content, and residual stress.

Phase behavior in thin films of weakly segregated block copolymer/homopolymer blends.

We have demonstrated the phase behavior of substrate-supported films of a symmetric weakly segregated polystyrene-block-poly (methyl methacrylate), P(S-b-MMA), block copolymer and its blends with homopolymer polystyrene (PS) at different compositions. Upon increasing the content of added PS in the blends, lamellae (L), perforated layers (PL), double gyroid (DG) and cylinders (C) are obtained in sequence for films. Among these nanodomains, PL and DG only exist in a narrow ϕPS region (ϕPS denotes the volume fraction of PS). At ϕPS = 64%, tuning film thickness and annealing temperature can produce parallel PL or DG with {121}DG lattice planes being parallel to the substrate surface. The effects of annealing temperature and film thickness on the formation of PL and DG are examined. In thin films with n ≈ 3 (n denotes the ratio of initial film thickness to inter-domain spacing), the PL phase solely exists regardless of temperature. However, for thick films with n ≈ 6 and 10, thermal annealing at the most accessible temperature produces films containing both PL and DG of various fractions, but a low temperature tends to favor a greater fraction of PL. The PL phase becomes the only discernible phase if thick films are shortly annealed at 230 °C.