Instability development of a viscous liquid drop impacting a smooth substrate

TL;DR

This study investigates the development of instabilities in viscous liquid drops impacting smooth surfaces, revealing how air pressure and viscosity influence the onset of instability and proposing a stress balance model.

Contribution

It introduces a model comparing air-induced destabilizing stress and viscosity-stabilizing stress, explaining different stabilization mechanisms in viscous and inviscid regimes.

Findings

Instability onset time decreases with air pressure as pressure^-2.

Instability onset time increases linearly with liquid viscosity.

The model shows a balance between destabilizing air stress and stabilizing viscosity stress.

Abstract

We study the instability development during a viscous liquid drop impacting a smooth substrate, using high speed photography. The onset time of the instability highly depends on the surrounding air pressure and the liquid viscosity: it decreases with air pressure with the power of minus two, and increases linearly with the liquid viscosity. From the real-time dynamics measurements, we construct a model which compares the destabilizing stress from air with the stabilizing stress from liquid viscosity. Under this model, our experimental results indicate that at the instability onset time, the two stresses balance each other. This model also illustrates the different mechanisms for the inviscid and viscous regimes previously observed: the inviscid regime is stabilized by the surface tension and the viscous regime is stabilized by the liquid viscosity.