ANALYSIS OF WATER DROP IMPACTS ON TILTED NON-WETTABLE SURFACES

ABSTRACT Normal and oblique impacts of water drops on dry solid surfaces were studied experimentally, to investigate the conditions for drop rebound. Although data from literature suggest that rebound of a drop from a surface can be achieved when wettability is low (i.e. contact angles are high), no clear quantitative criterion exists to predict when a drop will rebound. As such, experimental tests were conducted to study impacts of millimetric water drops on different dry solid hydrophobic and superhydrophobic surfaces, with different wettability characteristics (i.e. with different advancing and receding contact angle, T A and T R , respectively, and contact angle hysteresis, 'T ). The study was focused at performing a phenomenological investigation of drop impact, at understanding in which conditions a drop rebound, and at evaluating drop rebound time (time shift between impact and detachment of the drop from the surface). Impacts were performed on horizontal and tilted surfaces, to evaluate the effect of surface inclination on drop impact outcome. Millimetric water drops were used (constant diameter,