Theoretical consideration of contact angle hysteresis using surface-energy-minimization methods

In recent years, advances in coating manufacturing processes have allowed wetting characteristics of a surface to be tuned with micro/nano morphologies. Today, complex surface geometries can be created with various surface treatment methods. These advances can be implemented in phase-change heat-transfer applications, such as condensation, which relies on droplet behavior on a surface. Therefore, it is important to gain a fundamental understanding of wetting characteristics of textured surfaces having different geometrical configurations. This can be accomplished by studying the behavior of a single droplet on a given surface. Drop shapes and behaviors are affected by surface energies of different interfacial surfaces and surface morphologies. Contact angle hysteresis (CAH) - which is the difference between advancing and receding angles - can be estimated by utilizing concepts of surface-energy minimization. This is essential in heat transfer applications, as parameters such as drop size and distribution in condensation heat transfer are determined by CAH. In this study, a mathematical model has been developed to estimate CAH on different surface geometries and degrees of wetting. Modeling results suggest that CAH increases with increasing degree of wetting. Further, CAH remains low at both high and low droplet contact angles, whether the surface is hydrophilic or hydrophobic.