Large area fabrication of tuned polystyrene/poly(methylmethacrylate) periodic structures using laser interference patterning

The fabrication of advanced architectures in poly(methylmethacrylate-co-styrene) (PMMA-S) copolymers (ranging from 12 to 66%, mol content of methylmethacrylate) using direct laser interference patterning is reported. For all copolymer compositions, two different regimes were observed. At low laser intensities, the irradiated surfaces swell up due to the formation of microbubbles that result from the degradation of the methylmetacrylate (MMA) component. While laser ablation produces concave holes, the swelling process permits fabrication of convex hemispherical dots. At higher intensities the bubbles release from the surface Forming a periodic micropored Structure. In addition, the laser fluence necessary to swell the polymeric surface (swelling threshold) does not depend on polymer composition. while the ablation threshold, which determines the transition to the periodic micropored structure, strongly depends oil the MMA content. This observation can be explained by the mechanical and chemical properties of the copolymer. The method provides a unique way to produce periodical structures protruding from the polymer surface