On the lack of influence of contact area on the solid–liquid lateral retention force

Abstract

We experimentally show that, unlike the solid–solid frictional force, the solid–liquid retention force is determined by interactions at the triple line rather than over the solid–liquid contact area, as predicted by theory. We have prepared drops whose triple line enclosed a uniform surface, a hydrophobic island, and topographical inhomogeneities, and measured the same retention force for all three cases. We have also studied the retention force on drops whose initial triple line was non-circumferential and measured different retention forces for different shapes, also as predicted by theory. The experiments with non-circumferential drops provide (1) another way to show that the retention force is not proportional to the contact area, and (2) a manner to falsify a recent theory on drop depinning.