Droplet pinning on the tilted surface processed by a grinding machine

Abstract

The study reports the experimental results of pinning/sliding water droplets onto tilted stainless steel substrates with different roughness and texture directions. The substrates were textured by a grinding machine. Droplets were dropped onto the substrate using a syringe. The distance between the needle and the substrate was varied from 20 mm to 200 mm. After impingement, the droplets pinned or slid onto the tilted surfaces in the parallel and perpendicular to the texture direction. For each substrate, the conditions of pinning or sliding of the droplet were obtained using the probability theory. It was established that, in contrast to the case of a water droplet on the surface with perpendicular scratches, the probabilities of droplet pinning on the polished surface and surface with parallel scratches were equal. The perpendicular scratches on the polished surface of stainless steel increased the probability of pinning a droplet by 20 %. The main fundamental result is to establish two spreading modes: with fragmentation and without fragmentation. The limiting cases in which water droplets divided into a few smaller droplets after impingement were obtained.