Superwetting of Structured Surfaces

Superwetting of structured surfaces, sometimes referred to as hemi-wicking, was studied both experimentally and theoretically. Structured substrates with regular arrays of square pillars or frustra were machined from graphite blocks and then treated to render them lyophilic. Liquids spread over these surfaces to produce noncircular wetting areas. If the channels between the features were made shallower or narrower, liquids wicked more and spread over a larger area. The inherent wettability of the graphite was relatively unimportant; large differences in the contact angles had little influence on the spreading. Practically, this means that, to achieve extensive coverage, near-zero contact angles are not required. A combination of the appropriate surface structure and moderate inherent wettability can effectively flatten liquids, spreading them over very large areas.