Droplet impact: Viscosity and wettability effects on splashing.

Affiliation

Department of Mechanical Engineering, York University, Toronto, ON M3J 1P3, Canada. Electronic address: [Email]

Abstract

OBJECTIVE : The wettability of a surface affects the splashing behavior of a droplet upon impact onto a surface only when surface exhibits either a very high or a very low contact angle. Viscosity affects the splashing threshold in a non-monotony way.
METHODS : To examine the roles of drop viscosity and surface wettability on splashing, a wide range of liquid viscosities (1-100 cSt), surface wettabilities (from hydrophilic to hydrophobic), drop velocities (0.5-3.3 m/s), and liquid surface tensions (∼20 and 70 mN/m) were examined. High speed imaging was used.
RESULTS : Wettability affects the splashing threshold at very extreme limits of the wettability i.e. at very high or very low contact angle values; however, the wettability effect is less prominent on spreading-splashing regime map. For drops of any surface tension impacting surfaces with any wettability, an increase in viscosity (up to ∼5 cSt or Reynolds number of 2000) promotes splashing; whereas using liquids with viscosities larger than 5 cSt, suppress splashing. We explained such behaviors using evolution of the lamella rim, dynamic contact angle, and velocity of the expanding lamella. Finally, to predict the splashing, we developed a general empirical relationship which explains all of ours, and previously reported data.

Keywords

Droplet splashing,Droplet velocity,Liquid surface tension,Liquid viscosity,Surface wettability,

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