Contact angle hysteresis analysis on superhydrophobic surface based on the design of channel and pillar models

Contact Angle Hysteresis (CAH) is critical to the hydrophobicity of a surface, which describes the dynamic characteristic of droplets. In this paper, two different micro-structured surfaces respectively with micro-channel and micro-pillar structures (20 samples for each structure, with a range of channel and pillar widths between 25 and 250 μm) were fabricated by mechanical micro-milling process to investigate the effect of structural parameters on hydrophobicity of surfaces. It was found that the solid fraction plays a decisive role for a surface in the transition from being hydrophilic to hydrophobic. Quantitative interpretation was conducted and a dynamic methodology was established based on the physical nature of the controllable motion of a droplet. The five key states of a droplet including the initial, pre-forward, forward, pre-backward and backward were the main focus of this research. The prediction results based on the established model showed good consistency with experiments. The proposed model can estimate the advancing and receding angles very well. The outcome of this research will lead to new methodologies for preparing hydrophobic surfaces with micro-machining technology and play an important theoretical guiding role in fabrication of superhydrophobic surfaces.