Dependence of Contact Angle on Gas Pressure

The dependence of liquid contact angle on the pressure in a gaseous mixture occurring in contact with the liquid has been considered on the basis of the general thermodynamic relations reported in the previous work for small although macroscopic bubbles and droplets. The cases of a sessile droplet brought in a direct contact with a gas occurring under a certain pressure and a sessile bubble formed by an inert carrier gas on a wall inside the liquid have been analyzed. Exact relations have been obtained taking into account the dissolution of the gases in the liquid upon increasing pressure. It has been shown that, under such conditions, the contact angle decreases as the pressure is elevated. Specific experimental data on the advancing contact angles for carbon dioxide–water and ethane–cyclohexane interfaces with the surface of 316 stainless steel [10] have been discussed and explained.