Effective interfacial tension of a film solidified during the collision of a molten wax droplet with a water surface

Abstract

We investigated collision processes of droplets of paraffin wax melt with a water surface. We found that when the water temperature is significantly lower than the melting temperature of the wax, a liquid droplet solidifies in the vicinity of the interface between the wax and water, and the solidified wax left on the water surface after collision exhibits diverse morphologies, including irregularly breaking films and petal-like films. Experimental results and rheological measurements indicate that at large falling distances and relatively high water temperatures, the wax deforms as a plastic fluid and expands in the form of a hemispherical sheet along with the water surface, forming a cavity. Under such conditions, a thin solidified film created at the interface gives an effective interfacial tension to the interface and suppresses its expansion. We derived the time evolution equations of the size and the thickness of a solidified film. These equations indicate that the effective interfacial tension is approximately determined by the film thickness and the yield stress of the wax.