Kinetic study of a swelling-induced network of folds in a cross-linked PS-PDMS film

Abstract

Solvent-induced mechanical instability in a cross-linked poly(styrene-block-dimethylsiloxane) (PS-PDMS) film attached to a rigid substrate was systematically investigated. Through swelling with appropriate solvent vapor, a unique network of folds could be constructed successfully without the wrinkle-to-fold transition. Instead, small holes resulting from the mesostructural organization of PS-PDMS formed as nuclei to induce formation and growth of invaginated folds resembling creases which then constructed a network of invaginated folds. A complete network of sharp folds could be obtained after the two edges of a valley were combined into a sharp fold. The morphology and kinetics were closely related to the solvent solubility parameter and saturated vapor pressure. We varied the ratio between a relatively good solvent vapor and a poor solvent vapor, and so produced a slower dynamic process to precisely control the surface morphology. Poorly ordered cylinders with varied sizes resulting from strong cross-linking and spatial restrictions imposed by the network of folds could be obtained.