Edge-driven collapse of fluid holes

Abstract

We study the stability and collapse of holes at the wall in liquid layers on circular bounded containers with various wettabilities. Three distinct wetting modes of the hole are observed, which are related to the wettability of the container: when the substrate and the inner wall of the container are superhydrophobic, a stable hole remains as the liquid volume is continuously increased until the liquid layer covers the entire substrate; when the substrate and the inner wall are hydrophobic, an eye-shaped hole remains stable as the projected area of the hole exceeds a critical value $A_c$ , however, the hole collapses if the liquid volume is further increased; when the substrate is superhydrophobic but the wall is hydrophilic, on increasing the liquid volume, the hole suddenly transfers into a circular hole and is pushed against the wall, leaving the hole dwelling around the centre of the container. Theoretical analyses and numerical simulations are conducted to establish the phase diagram for different wetting modes. It is found that, in the second mode, $A_c$ increases with the size of the container but decreases with the contact angle of the substrate and the wall. Furthermore, we experimentally investigate the dynamics of the hole. The time evolution of the area of the hole obeys a scaling relationship $A \sim (t_0 - t)^{1.1}$ after the hole collapses at time $t_0$ .