Toward Surfaces with Droplet Impact Robustness and Low Contact Angle Hysteresis

Abstract

Superhydrophobic surfaces show excellent water repellent performance. However, liquid impalement occurs when a droplet impacts on the surface at high velocity. To achieve higher resistance to liquid impalement at the same scale, a dense array of structures or structures with pinning at the structures top are typically used, but they also lead to increased contact angle hysteresis and higher energy dissipation. Changing the structure side wall shape can help to maintain low hysteresis and withstand high impact energy at the same scale. Droplet contact angle, contact angle hysteresis and droplet impact experiments are performed on both conical and cylindrical pillar surfaces. Comparing conical and cylindrical pillar structures with the same pitch and height, it is found that cylindrical pillars exhibit higher critical Weber number but result in larger contact angle hysteresis and larger liquid residue size when above a critical Weber number. A proper design of conical structures can maintain large contact angle, low hysteresis, strong resistance to impalement, higher number of bouncing and smaller liquid residue size. In addition, the critical Weber number for the conical structures in this work is higher than micro-patterned pillar surfaces at the same pitch range, implying that we improve the anti-wetting performance further.