Measurement of Lateral Adhesion Forces at the Interface between a Liquid Drop and a Substrate

A novel instrument allows for the first time measurements of the lateral adhesion forces at a solid-liquid interface, f_∥, in a way that is decoupled from the normal forces, f_⊥. We use it to measure how f_∥ between a drop and a surface is influenced by different f_⊥ and different histories of drop resting periods on the surface prior to sliding, t_rest. The variation of f_∥ with t_rest is similar for different f_⊥ and always plateaus as t_rest→∞. We show that the f_∥ plateau value is higher when f_⊥ is lower. This seemingly counterintuitive result is in agreement with recent theories.