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 disco ntinuity lying on the boundary between two surfaces with different wet tabilities. We examine here the case of a non-rectilinear boundary whi ch is the most frequent case as has been shown by AFM. The observation of liquid fronts pinned on the frontier shows different kinds of beha viour: either the liquid follows the exact profile of the boundary eve n at a small scale, or it is only partially anchored. We propose a the oretical model in the case of a purely sinusoidal boundary, that predi cts four different regimes of pinning. The experimental study, which n eeded the preparation of such model systems, confirmed the main result s of the model. In particular, we have shown that the most important p arameter is the product of the amplitude of the sinusoid and its wavev ector.