Behaviour of sessile drops revealed in ‘car crash’ like impact

Abstract

This study reports the effect of impact forces on the behaviour of sessile drops when their rapid horizontal displacement is abruptly abrogated. The experimental setup is akin to “car crash” simulation, wherein an object is moved linearly at a predetermined speed and then brought to a complete stop by colliding with a stationary obstacle. The mechanical translator used allowed drops to attain consistent speeds prior to imposition of an impact force. In investigations on binary mixtures comprising glycerol-water (0–100% vv) and polyvinyl alcohol – water (0–10% vv), it was found that the positions as well as the contact angles of the advancing and receding contact lines could alter in tandem. The trajectories from a new phase-space representation for binary mixtures of varied compositions indicated that drop behaviour as a function of contact angle and positional displacement differed between the advancing and receding contact lines in order to dissipate the impact energy applied. The experimental results scaled well with Ohnesorge numbers but not Bond or Weber numbers, indicating a dominant effect played by viscosity. The approach here offers new vistas in viscosity determination of fluids, and in the study of drops subjected to evaporation and freezing conditions.