Microfabricated textured surfaces for super-hydrophobicity investigations

The natural hydrophobicity of surfaces can be enhanced if they are micro-textured. This is due to air trapped in the structure, which provides the deposited drop with a composite surface made of solid and air on which it is resting. Here, we give evidence for this effect using a forest of micro-pillars which allows us to control the micro structure density under the drop, and thus the degree of super-hydrophobicity. For this purpose, silicon wafers were firstly patterned by conventional photolithography techniques. After deposition of an aluminium layer, the samples were subjected to a deep reactive ion etching (DRIE) with the ''Bosch process'' in order to achieve high aspect ratios (>=10). However, this state is not always the most stable situation for a drop on a hydrophobic surface: the drop can also fill up the microstructure. We have been able to observe these two super-hydrophobic states on our surfaces and to characterize advancing and receding contact angles for both of them.