Strategies for void-free liquid filling of micro cavities

We demonstrate that geometrically sharp edges, a common feature of many microfabricated structures, play an important role in their capillary filling behaviour. Depending on the opening angle of the edge and the contact angle two situations may occur. The liquid may be hindered to cross the edge or it may drawn into the edge by a singular capillary pressure. We demonstrate these effects by some basic experiments and show how these principles may be used to ensure void free liquid filling of microfluidic structures even in the presence of roughness-induced contact line pinning.