Droplet Impinging Behavior on Surfaces with Wettability Contrasts

Bahador Farshchian, Ingram School of Engineering, Texas State University, San Marcos, TX 78666, USA.
Jacoby Pierce, Ingram School of Engineering, Texas State University, San Marcos, TX 78666, USA.
Mohammad S. Beheshti, Department of Mechanical and Industrial Engineering, Center for Bio-Modular Multiscale Systems for Precision Medicine, Louisiana State University, Baton Rouge, LA 70803, USA.
Sunggook Park, Department of Mechanical and Industrial Engineering, Center for Bio-Modular Multiscale Systems for Precision Medicine, Louisiana State University, Baton Rouge, LA 70803, USA.
Namwon Kim, Ingram School of Engineering, Texas State University, San Marcos, TX 78666, USA.

Abstract

Heterogeneous substrates with moderate and extreme wettability contrasts were fabricated by comprising of superhydrophobic/hydrophilic and superhydrophobic/extremely hydrophilic surfaces, respectively. The interactions of water droplets impinging on the surfaces with sharp wettability contrasts were investigated experimentally. The impinging droplets that slightly touch the hydrophilic or extremely hydrophilic areas on each substrate exhibit a directional rebounding towards the more wetting surfaces, i.e., hydrophilic or extremely hydrophilic surface. The trajectory and landing distance of the rebounded droplets were tailored by controlling the releasing height of the droplet, wetting contrast across the border, and portion of the droplet touching the more wetting surface of the substrates with wettability contrasts. The landing distance of the droplet increases with the increased releasing height and higher wettability contrast across the border. Increasing the portion of the impinging droplet touching the more wetting surface of the heterogeneous substrates leads to the shorter landing distance of rebounded droplets.