Design of lotus-simulating surfaces: Thermodynamic analysis based on a new methodology

Superhydrophobicity has increasingly attracted the specialists’ attention owing to its inspiring applications. Currently, superhydrophobic surfaces have been prepared by different techniques. However, microscopic mechanisms responsible for contact angle hysteresis (CAH) and free energy barrier (FEB) are not yet completely clear. In this study, we propose an intuitive free energy (FE) thermodynamic analysis on superhydrophobic surfaces with a micro-/nano-scale pillar structure based on a new method with the purpose of determining and explaining CAH with use of changes in free energy (CFE) and FEB. The relationships between CA, CAH, CFE, FEB and micro-/nano-structure parameters are established by numerical simulation. The dependency of the hydrophobicity on the micro-/nano-scale is quantitatively discussed. Based on changes in FEB, the possible transition from non-composite to composite wetting state is innovatively developed. These will play an important theoretical guiding role in fabrication of superhydrophobic surfaces.