Dynamic characteristics of water spreading over laser-textured aluminum alloy surfaces

Abstract

Laser texturing has great potential for controlling wetting properties as well as spreading dynamics of liquid small volumes on technological metal surfaces. In this work, nanosecond pulse laser was used to create some ordered and anisotropic textures on aluminum alloy surfaces. The dynamic characteristics and contact angle hysteresis were obtained by increasing and decreasing the droplet volume. In this wetting/dewetting cycle, we recorded fluctuational movements of the three-phase contact line over the surfaces with an ordered texture when the capillary number tends to zero. These movements are caused by activity of forces leading to fluid circulation in the droplet, as well as inertia and gravity. To determine the contact angle hysteresis when the three-phase contact line fluctuates, we developed a new approach. We showed that the contact angle hysteresis depends on the droplet state (the presence of air cushions in the cavities in a thin near-surface layer) largely than on the roughness. We found the influence of repeated wetting cycles (multiple advancing and receding liquid movement) on the dynamic characteristics of water spreading over the laser-textured aluminum alloy surfaces. The molecular-kinetic and hydrodynamic models were used to interpret the liquid movement over the surfaces with ordered and anisotropic textures.