INERTIAL RETRACTION OF LIQUID FILM ON MODERATELY WETTABLE PLATE

Spreading and rebounding of drop on solid substrate are of great significance in industry and scientific research, where the evolution of morphology of a drop is investigated frequently. It is normally believed that a spread drop retracts in inertia-capillary regime with a speed deduced by a Taylor-Culick procedure. Experimental and finite element method studies were conducted, which show that a drop retracts on moderately wettable plate with a low speed after the aforementioned inertia-capillary retraction. The speed has a value as low as 1/10 of the first retracting stage. The mechanism is explored according to the experiments and additional numerical simulations. It is found that the low-speed retraction depends on the density and capillary of the liquid, rather than the viscosity and wall condition (including the wettability and slip characters). It is revealed that the process is still dominated by capillary-inertial effects. The findings are also validated on the liquid with viscosity as high as 10 times of the original one in simulations. The research is valuable for studying droplet dynamics and relative industrial processes.