Protecting sub-micrometer surface features in polymers from mechanical damage using hierarchical patterns

Micro and nano textures on surfaces have shown outstanding properties in several natural examples. Especially, contact properties are in the focus of science including wetting properties, bacteria and cell adhesion of textured surfaces. A critical point of these patterned surfaces is related to the relative low mechanical resistance to scratches, especially when sub-micrometer features are required to provide an enhanced function, such low bacteria adhesion. Therefore, new topographies capable to protect the damage of the sub-micrometer features are necessary. In this work, hierarchical surface patterns are produced on polyimide substrates with the aim of reducing wear of the small scaled features. The hierarchical surface structures are fabricated using Direct laser interference patterning, employing a ns-pulsed Nd:YAG laser, with spatial periods of 0.5 mu m and 5 mu m. Two and three beam interference setups have been employed, producing surfaces with post-like and hole-like patterns. The wear experiments are performed with 1.5 mm 100Cr6 steel ball oscillating over the surface up to 1000 cycles loaded with 40 mN. The textured surfaces are also characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM). It was found, that hierarchical patterns consisting on holes with 0.5 mu m and 5.0 mu m periods can protect the sub-micrometer patterns significantly from mechanical damage and thus prolonging their lifetime.