Dynamics and depinning of the triple contact line in the presence of periodic surface defects

We propose an equation that describes the shape of the driven contact line in dynamics in the presence of an arbitrary (possibly random) distribution of the surface defects. It is shown that the triple contact line depinning differs from the depinning of interfaces separating two phases; the equations describing these phenomena have an essential difference. The force--velocity dependence is considered for a periodical defect pattern. It appears to be strongly nonlinear both near the depinning threshold and for large contact line speeds. This nonlinearity is comparable to experimental results on the contact line depinning from random defects.