Water Drop on Thin Viscous Oil Layers: From Stick-Slip Spreading to Dewetting

TL;DR

This study explores how water droplets spread and dewet on thin viscous oil layers, revealing stick-slip spreading at low impact energies and long-term oil dewetting dynamics, with implications for practical and fundamental understanding.

Contribution

It provides new experimental insights into the impact-driven and long-term spreading behaviors of water on viscous oil layers, highlighting the role of dewetting dynamics.

Findings

Stick-slip dynamics occur at low impact energies.

Spreading behavior becomes smooth at higher impact energies.

Long-term spreading governed by oil dewetting, independent of impact energy.

Abstract

The impact of water droplets on thin layers of immiscible viscous liquids, such as oil films, is commonly encountered across contexts ranging from kitchen activities to industrial processes. In this study, we experimentally investigate the short-term and long-term behavior of water drops spreading on silicone oil-coated surfaces. During the initial spreading, especially towards zero impact energies, the drop edge exhibits stick-slip dynamics, characterized by intermittent stops. The stick-slip behaviour diminishes with increasing spreading energy from impacts, where the drop spreads without noticeably displacing the oil layer. In the long-term dynamics, regardless of whether the spreading is gradual or impact-driven, the drop eventually spreads onto the surface under the oil layer, governed by the dewetting dynamics of the oil. The delay for the second spreading is independent of the Weber number, indicating that the impact initially does not significantly deform the oil layer. Our findings provide new insights into the dynamics of water-oil interactions, with implications for both practical applications and fundamental research.