Dynamics of a stick-jump contact line of water drops on a strip surface.

In this study, we prepared microscale periodic rough structures consisting of parallel strips on a silicon surface. The width of each strip was equal to the gap between the strips, and the silicon surface was silanized with perfluorooctyltrichlorosilane. We studied the wetting characteristics of water drops as they advanced and receded on patterned surfaces in a direction perpendicular to the strip. Water drops were observed to advance or recede in a smooth manner when the strip width was smaller than 32 microm but in a stick-jump manner when the strip width was larger than 50 microm. The regular strip-patterned substrates enabled us to deduce the relationship between the stick-jump behavior and the feature size of the substrate. For surfaces on which water drops showed stick-jump behavior, the oscillation amplitude of the contact angle decreased with decreasing strip width. In addition, the jumping distances of the contact lines, for both advancing and receding water drops, were nearly equal to the strip period. A 2D model was applied to analyze the contact line motion on the patterned surfaces, which showed reasonable agreement with the experimental results.