Regensburg 2013 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 30: Poster: Focus: Wetting on smooth and rough surfaces: From spreading to superhydrophobicity

CPP 30.10: Poster

Wednesday, March 13, 2013, 16:30–18:30, Poster C

Microcones and Nanograss: Towards mechanically robust superhydrophobic surfaces — •Vitaliy Kondrashov and Jürgen Rühe — University of Freiburg, Freiburg, Germany

We report on the generation of superhydrophobic surfaces, which are resistant to strong mechanical forces, especially against high shear stress. To this we generate surfaces, which have two roughness levels: micrometer sized silicon microcones surrounded by superhydrophobic silicon nanograss. The fabrication process of the surface is mask-free, and both microcones and nanograss are fabricated in consecutive processes by Deep Reactive Ion Etching (DRIE) in the overpassivation regime. Varying the process parameters, microcones of different size and density were fabricated, while nanograss size and distribution were kept constant.

When shear is applied, the microcones take the load and prevent contact of the shearing surface with the mechanically instable silicon nanograss. As the microcones can cause pinning of the contact line, the height and density of the microcones are important parameters for the influence of wear onto the wetting properties. As result, the shear-stress experiments show that surfaces with high density of large microcones are able to sustain high shear loads without noticeable loss in superhydrophobicity. However, the larger the microstructures the larger shaved hydrophilic area which increases pinning to the drop. This shows that, the control over microcones size and density is a key factor in realization of mechanically robust superhydrophobic surfaces.