Ring-Shaped Sessile Droplet

It is recognized that small liquid droplet placed on the solid substrate forms equilibrium contact angle that can be obtained from well-known Young’s law. Previously, deviations from Young’s law were demonstrated for the droplets exposed to external fields (gravity, electric, etc) and for the droplets on non-homogeneous substrates. This work reveals that the Young’s equilibrium contact angle can be altered by geometrical reasons only. We consider a ring-shaped droplet on a solid substrate as a test structure for our discussion. We use the global energy consideration for analysis of system equilibrium for the case of freely deposited liquid with no external forces applied. The theoretical analysis shows that steady ring-shaped liquid structure on a solid substrate does exist with contact angles on both contact lines to be different from the Young’s equilibrium contact angle. This material is based on research sponsored by the Defense Microelectronics Activity (DMEA) under agreement H94003-09-2-0905.