Superhydrophobic elastomer surfaces with nanostructured micronails

New approaches to the fabrication of microstructures of special shape were developed for polymers. Unusual superhydrophobic surface structures were achieved with the use of flexible polymers and hierarchical molds. Flexible polyurethane-acrylate coatings were patterned with microstructures with use of microstructured aluminum mold in a controlled UV-curing process. Electron microscope images of the UV-cured coatings on polymethylmethacrylate (PMMA) substrates revealed micropillars that were significantly higher than the corresponding depressions of the mold (even 47 vs. 35 mu m). The elongation was achieved by detaching the mold from the flexible, partially cured acrylate surface and then further curing the separated microstructure. The modified acrylate surface is superhydrophobic with a water contact angle of 156 degrees and sliding angle of <10 degrees. Acrylic thermoplastic elastomers (TPE) were patterned with micro-nanostructured aluminum oxide molds through injection molding. The hierarchical surface of the elastomer showed elongated micropillars (57 mu m) with nail-head tops covered with nanograss. Comparison with a reference microstructure of the same material (35 mu m) indicated that the nanopores of the micro-nanomold assisted the formation of the nail-shaped micropillars. The elasticity of the TPE materials evidently plays a role in the elongation because similar elongation has not been found in hierarchically structured thermoplastic surfaces. The hierarchical micronail structure supports a high water contact angle (164 degrees), representing an increase of 88 degrees relative to the smooth TPE surface. The sliding angle was close to zero degrees, indicating the Cassie-Baxter state. (C) 2011 Elsevier B.V. All rights reserved.