TOTAL OR PARTIAL PINNING OF A DROPLET ON A SURFACE WITH A CHEMICAL DISCONTINUITY

We present a study of the pinning of a contact line on a surface discontinuity lying on the boundary between two surfaces with different wettabilities. We examine here the case of a non-rectilinear boundary which is the most frequent case as has been shown by AFM. The observation of liquid fronts pinned on the frontier shows different kinds of behaviour: either the liquid follows the exact profile of the boundary even at a small scale, or it is only partially anchored. We propose a theoretical model in the case of a purely sinusoidal boundary, that predicts four different regimes of pinning. The experimental study, which needed the preparation of such model systems, confirmed the main results of the model. In particular, we have shown that the most important parameter is the product of the amplitude of the sinusoid and its wavevector.