Role of anisotropic pinning and liquid properties during partial rebound of droplets on unidirectionally structured hydrophobic surfaces

Droplet Rolling Dynamics over a Hydrophobic Surface with a Minute Width Channel

Unidirectional and stabilize droplet rolling over hydrophobic surfaces is critical for self-cleaning applications of large areas. Introducing minute size channels on hydrophobic surfaces in the droplet rolling direction can minimize droplet wobbling and enables unidirectional rolling. The droplet rolling behavior over an inclined hydrophobic surface having a minute size channel is investigated. The flow field developed inside the droplet fluid is numerically simulated in a three-dimensional domain pertinent to experimental conditions. Experiments are carried out using a high-speed facility to monitor and evaluate droplet motion over channeled and flat hydrophobic surfaces. The findings revealed that predictions of the droplet translational velocity and those obtained from the experiments are in good agreement. The presence of a minute channel on the hydrophobic surface gives rise to droplet fluid inflection into the minute channel, which in turn modifies the center of mass of the droplet during rolling. This lowers the droplet wobbling height and enables the droplet to roll unidirectionally along the channel length. Enlarging the channel width on the hydrophobic surface increases droplet kinetic energy dissipation while reducing the droplet rolling speed. The complex flow structures formed in the droplet fluid modifies the pressure along the droplet centerline; however, the droplet fluid pressure remains almost the same order as the Laplace pressure in the upper region of a rolling droplet over the channeled hydrophobic surface.