Regensburg 2016 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 46: Poster: Wetting, Nano- and Microfluidics

CPP 46.11: Poster

Wednesday, March 9, 2016, 18:15–21:00, Poster B2

Geometry induced asymmetric contact angles — •Bang-Yan Liu — National Taiwan University, Department of Chemical Engineering, 10617 Taipei, Taiwan — Saarland University, Experimental Physics, D-66041 Saarbrücken, Germany

Triangle post decorated surfaces were studied in this research. Triangular posts were arranged in square lattice and made from PDMS. Asymmetric contact angles were observed, both advancing and receding contact angle in triangle base direction were higher than that in the tip direction. Structures with various triangle sizes and post heights were examined and the three-phase contact line motion was analyzed to study this phenomenon. As water spreading, a strong pinning always happened on the outermost edges of triangular post structure related to droplet center, and with the increase of structure edge presence in three-phase contact line, advancing contact angle raised dramatically. The geometry difference of triangle tip and base resulted in different edge presence of three-phase contact line and caused contact angle asymmetry. However, when the structure height grew, advancing contact angle of both directions increased, and the asymmetry was reduced. On the other hand, de-wetting showed different behavior. Three-phase contact line pinned on the inner edge of structure and one-by-one depinning behavior was observed. Receding contact angle happened when the retreating three-phase contact line depinned from the very last structures to another row of structures. By designing and tuning structure geometry, an easy-produced asymmetry surface can be obtained.