Assessment criteria for superhydrophobic surfaces with stochastic roughness

We describe a comprehensive measurement and analysis methodology for effectively predicting, defining, and controlling the structural and wetting properties of stochastically rough superhydrophobic surfaces. Specific roughness analysis procedures are based on Power Spectral Density (PSD) functions determined from topography data and subsequent data reduction processes. It is shown that these functions and a subsequently derived "wetting" parameter are capable of linking the roughness and wetting properties, whereas conventional roughness parameters fail. For predictions of the wetting behavior, advancing and receding contact angles as well as slide-off/roll-off angle measurements are performed. Examples of natural and technical applications comprise a Lotus leaf and thin film coatings with stochastic nanoroughness. These surfaces reveal high advancing contact angles, low contact angle hysteresis, low roll-off angles, and, consequently, the self-cleaning effect.