Contact-angle-hysteresis effects on a drop sitting on an incline plane

Abstract

We study the contact-angle hysteresis and morphology changes of a liquid drop sitting on a solid substrate inclined with respect to the horizontal at an angle α. This one is always smaller than the critical angle, αcrit, above which the drop would start to slide down. The hysteresis cycle is performed for positive and negative α´s (|α|<αcrit), and a complete study of the changes in contact angles, free surface, and footprint shape is carried out. The drop shape is analyzed in terms of a solution of the equilibrium pressure equation within the long-wave model (lubrication approximation). We obtain a truncated analytical solution describing the static drop shapes that is successfully compared with experimental data. This solution is of practical interest since it allows for a complete description of all the drop features, such as its footprint shape or contact angle distribution around the drop periphery, starting from a very small set of relatively easy to measure drop parameters.