Thin Film Formation During Splashing of Viscous Liquids

TL;DR

This paper investigates the dynamics of thin film formation during viscous liquid splash impacts, highlighting the roles of ambient gas, impact velocity, and air entrainment in the splash process.

Contribution

It provides new insights into the mechanisms of thin sheet ejection and air bubble entrapment during viscous drop impacts, emphasizing the influence of ambient gas conditions.

Findings

Thin sheet ejection time depends on impact velocity, viscosity, gas pressure, and molecular weight.

Air bubbles are trapped below the drop and entrained under the lamella during splash.

Air entrainment stops at a lamella velocity independent of impact velocity and gas pressure.

Abstract

After impact onto a smooth dry surface, a drop of viscous liquid initially spreads in the form of a thick lamella. If the drop splashes, it first emits a thin fluid sheet that can ultimately break up into droplets causing the splash. Ambient gas is crucial for creating this thin sheet. The time for sheet ejection, $t_{ejt}$, depends on impact velocity, liquid viscosity, gas pressure and molecular weight. A central air bubble is trapped below the drop at pressures even below that necessary for this sheet formation. In addition, air bubbles are entrained underneath the spreading lamella when the ejected sheet is present. Air entrainment ceases at a lamella velocity that is independent of drop impact velocity as well as ambient gas pressure.