Laser surface texturing for superhydrophobic, icephobic and friction reduction functionalization

Abstract

Nanometre and/or micrometer scale periodic features naturally present decorating the skin of many insects, fishes or plants have been found to give them extraordinary aesthetic, adhesion, antifouling, wear resistance, superhydrophobic or drag reduction properties. With the aim of artificially conveying the same properties to products and tools, researchers have tried to reproduce such bionic topography on the surface of a huge variety of materials using different manufacturing methods. Among the different manufacturing technologies, surface texturing based on direct laser writing using ultrashort pulses offers great flexibility in terms of geometry and size of the feature to be created. This work will focus on two specific types of functionalization of metallic as well as rubber surfaces through laser surface texturing, i.e., icephobicity and friction reduction. In the first case, different texture patterns were laser written on sheet samples of Aluminum Alloy of interest for aerospace applications. Their wettability and anti-icing properties were investigated through water contact angle experiments in different environmental conditions and steam-freezing experiments were conducted in a climate chamber. The role of the laser textured pattern geometry on the frictional performances of a rubber surface under lubricated non-conformal as well as conformal point contact has been also widely investigated. In the first case, no improvements were obtained in terms of frictional performances, ascribable to the reduced number of dimples involved in the contact area. Conversely, remarkable friction reduction was achieved in mixed and in the transition between the mixed and the elasto-hydrodinamic lubrication regime, thanks to the concurrence of several effects as micro-cavitation, wear debris trapping, and lubricant entrapping within the texture.