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.