Review of Fluid Slip over Superhydrophobic Surfaces and Its Dependence on the Contact Angle

A review of the characteristics of hydrophobicity is presented, with the goal of investigating the relationship, if any, between the contact angle (a macroscopically observed property) and the slip length (a microscopic phenomenon). An analysis of simulations, and of their evolution through the years, sheds light on some inherent differences between contact angle and slip length behavior on flat and patterned surfaces. Previous studies lead to the conclusion that epitaxial layering of fluid near the solid is intricately related to the magnitude of fluid slip. Epitaxial layer data help to explain unexpected slip length behavior in relation to the contact angle, and reported inconsistencies between slip length experiments and simulations. Therefore, it seems that solids that can produce favorable epitaxial layering of the fluid will cause larger slip. Dimensional analysis is used to elucidate the contact angle−slip length relationship. Results can be applied to the development of artificial supersolvophobic surfaces that would exhibit predictable fluid slip with important practical applications.