Long term superhydrophobic and hybrid superhydrophobic/superhydrophilic surfaces produced by laser surface micro/nano surface structuring

Stable superhydrophobic and superhydrophilic surfaces were created using laser surface micro/nano patterning. These were based on periodic 3D micro/nanostructures produced on 316L stainless steel over large areas using nanosecond and picosecond laser surface fabrication. The effects of laser processing parameters on controlling the micro-/nano-topographical characteristics of 24 different types of structures were presented. Surface roughness, surface chemical composition and wettability (via water contact angle) of these surfaces were characterised. Aging experiments were carried out for up to 8 months to analyse the durability of the prepared surfaces under three conditions of water (hot, normal and icy). Samples with superhydrophobic characteristics, processed with the ps or ns lasers in air, kept dry (water repellent) for over 8 months when tested in ice water ( degrees C-4 degrees C), whilst those stored in hot water (80 degrees C) or room temperature water could only be kept dry for 3-14 weeks. Samples processed in water had shorter water repellent life and samples processed with the ns laser in air had the longest water repellent periods. The hybrid superhydrophobic and superhydrophobic surfaces had a stability life for water repellent and water spreading of over 6 months.