Nonaxisymmetric drop shape analysis and its application for determination of the local contact angles

Abstract

We describe here a numerical method for finding the local contact angles of a drop in the case of partial wetting for given values of the drop volume and capillary length when there are data available for the whole contact line of the drop. There are no special restrictions imposed on the type of the contact line: the solid substrate on which the drop rests can be heterogeneous or rough or both, it can be horizontal or tilted. The method is intended to be used in conjunction with experimental results similarly to the axisymmetric drop shape analysis-diameter (ADSA-D) and analysis-profile (ADSA-P) methods. The numerical method is essentially an iterative minimization procedure based on the local variations approach. It allows finding drop shapes which are not axially symmetric. The contact angles are then determined from the obtained shape of the drop. Several examples of applying the method are described for a drop on: flat, horizontal but heterogeneous substrate; flat, tilted substrate, and grooved horizontal substrate.