Paper detail

Determining superhydrophobic surfaces from an expanded Cassie Baxter equation describing simple wettability experiments

The characterization of the wetting on superhydrophobic surfaces is rather complex. Usual contact angle experiments are difficult to perform and the lateral movement of droplets as well as the pinning at point defects on the surface can disturb the measurements. Even if precise contact angle measurements can be performed the information gain is limited if the surface is heterogeneously wetted. This results in the possibility of two surfaces with different roughness, different surface energy and thus different underlying wetting mechanisms exhibiting the same contact angle. We introduce the utilization of dynamic wetting experiments as an additional surface probe which allows a better characterization of superhydrophobic surfaces. A theoretical model is presented which describes the spreading of water jets on a superhydrophobic surface and allows the determination of the wetted fraction of a heterogeneously wetted superhydrophobic surface. The determined values for the wetted fraction identify a common problem when building artificial super hydrophobic surfaces and can fundamentally improve their understanding.