Wetting Transition of the Ethanol–Water Droplet on Smooth and Textured Surfaces

Abstract

The wetting behavior of an ethanol–water droplet is investigated on graphitic smooth and rough surfaces using molecular dynamics simulations. On a smooth surface, ethanol molecules prefer to stay at the vapor–liquid and solid–liquid interfaces. The contact angle of a droplet on a smooth surface decreases with an increase in the ethanol concentration from 0 to 30 wt %. The corresponding line tension increases from 3 × 10–11 to 9.4 × 10–11 N at 300 K. The critical weight percentage for complete wetting is found to be approximately 50%. In the case of a textured graphite surface, with the addition of ethanol molecules, the Cassie–Baxter state of a drop is transformed into the Wenzel state via the partial Wenzel state, with ethanol molecules filling the rough region, leading to an increase in its wettability. A linear relation of 1 + cos θ with the roughness parameter associated with the Cassie–Baxter and Wenzel states is observed, indicating that the solid–liquid interfacial tension is directly proportional to the roughness parameter. This behavior is akin to that seen for the case of pure liquid. The hydrogen bonding and density profile are analyzed to understand the wetting states of the blended drop.