Surface Wrinkling on Polymer Films.

A series of gold precursor solutions are prepared by dissolving HAuCl 4 and its mixtures with K 2 CO 3 of different contents in deionized (DI) water. Neat HAuCl 4 predominately forms AuCl 4 - ions in an aqueous solution. In the presence of K 2 CO 3 , AuCl 4 - ions hydrolyze to form [AuCl 4- x (OH) x ] - complex ions. Increasing the content of K 2 CO 3 in a gold precursor solution increases the content of [AuCl 4- x (OH) x ] - complex ions and decreases the content of AuCl 4 - ions. Poly(4-vinyl pyridine) (P4VP) films of two different molecular weights are deposited on SiO x /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, AuCl 4 - ion content, and residual stress.