Droplet hysteresis investigation on non-wetting striped textured surfaces: A lattice Boltzmann study

The Cassie–Baxter model is widely used to predict the apparent contact angles on textured super-hydrophobic surfaces. However, it has been challenged by some recent studies, since it does not consider contact angle hysteresis and surface structure characteristics near the contact line. The present study is to investigate the contact angle hysteresis on striped textured surfaces, and its elimination through vibrating the substrate. The two-phase flow is simulated by a recently proposed lattice Boltzmann model for high-density-ratio flows. Droplet evolutions under various initial contact angles are simulated, and it is found that different contact angles exist for the same textured surface. The importance of the contact line structure for droplet pinning is underlined via a study of droplet behavior on a composite substrate, with striped textured structure inside and flat structure outside. A “stick–jump” motion is found for the advancing contact line on the striped textured surface. Due to hysteresis, the contact angles after advancing are not consistent with the Cassie–Baxter model. The stable equilibrium is obtained through properly vibrating the substrate, and the resulted contact angles are consistent with Cassie’s predictions.