Experimental study of droplet splashing phenomena on hydrophobic micro-and micro/nano-textured surfaces

Droplet splashing phenomena are observed experimentally on the well-designed hydrophobic micro and micro-/nano-textured surfaces. The critical Weber numbers ( We cr ) for splashing are investigated by considering the geometrical surface conditions. The splashing was facilitated with large micropillar spacing and diameter and suppressed with small ones. Large pillar spacing and diameter enabled easy penetration of liquid by reduced capillary force and increased the outlet of airflow. This air-liquid velocity difference creates instability at the edge of the spreading droplet, thereby generating splashing based on the Kelvin-Helmholtz instability mechanism. Besides, earlier splashing was observed on micro/nano textures than on microtextured surfaces. Since the impacting droplet could not penetrate the nanopillars due to higher capillary pressure and slip boundary condition formation, it reduces airflow friction. Hence an increase in the air-liquid velocity ratio renders splashing.