Wettability of surfaces with different surface microstructures textured by laser

Abstract

In order to study the effects of working conditions and solid surface topography on the wettability of material, a series of No. 45 steel specimens with the same surface arithmetic average height Sa and different surface microstructures is designed and manufactured by laser surface texturing. All the surfaces are measured by a non-contact three-dimensional (3D) optical profiler Talysulf CCI Lite and characterized by the ISO25178. A series of wetting experiments is carried out with the No. 32 turbine oil on an optical contact angle and surface tension meter SL200 KS. The effects of temperature, droplet volume and surface structure on the wettability are analyzed. Meanwhile, quantitative research of the relationship between the random characteristics of topography and wettability of the solid surface is conducted with parameters obtained from the ISO25178. Based on the fact that the contact angle is an acute angle, the results show that the contact angle of the droplet on the solid surface decreases rapidly to a stable value in the wetting process. The stable value decreases with the increase of the temperature, while it first increases and then decreases with the increase of the droplet volume. The surface wettability can be affected by the laser micro-texturing. Surfaces with similar values of Sa show different wettabilities for different micro-textures with different shapes and directions. Textured surfaces with grooves along the spreading direction of the droplet perform the best wettability in our research. Results also predicate that the wettability of surface is greatly influenced by the amplitude parameters (Sku, Ssk), spatial parameters (Str, Sal), hybrid parameters (Sdq, Sdr), and feature parameters (Sda, Sdv), which are all obtained from the ISO25178. The wettability of hydrophilic surface becomes better with increasing Sku, Sal, and Sdr and reducing Ssk, Str, and Sdq.