Self-organized swelling of a metal-capped polymer thin bilayer

Abstract

We report on the formation of self-organized surface patterns on a thin metal film capped polymer bilayer on a substrate by swelling. The self-organization is directed by a periodically corrugated elastomeric mold which exerts a nodal effect that confines the intrinsic swelling wave, and the resulting self-organized patterns are anisotropic and quite periodic. The corrugated pattern confined by the elastomeric mold was observed from the earlier stages of swelling while the small wrinkles (the first self-organized pattern) were formed in the later stages of the swelling. The temporal evolution of the first self-organized pattern was analyzed theoretically on the basis of the wave interaction relationship between the intrinsic swelling wave and the periodic corrugation formed in the earlier stages, and the experimental data were well-matched with the results of the analysis. The maximum value of the harmonic number for the wave number of the corrugated pattern was also analyzed. The strain in the metal thin film increases with increasing swelling time and arrives at a state of mechanical equilibrium (strain growth rate ∼0). The growth rate and moment of arrival of the strain at the state of mechanical equilibrium were different for the metal films on the ridge and groove of the corrugated pattern. In the case of the self-organized swelling directed by a periodically corrugated elastomeric mold with a relatively large line width, irregular wrinkles or twisted patterns (the second self-organized pattern) were observed which were easily distinguished from the corrugated patterns by the pattern replication and the first self-organized swelling patterns. ？ 2007 American Chemical Society.