Short time dynamics of viscous drop spreading

TL;DR

This study investigates the very early stages of viscous drop spreading on solid surfaces, revealing a logarithmic decrease in spreading velocity and minimal influence from contact line dissipation, using high-speed imaging for detailed analysis.

Contribution

It provides new experimental insights into the initial spreading dynamics of viscous drops, showing a non-power-law behavior and the insignificance of contact line effects during early stages.

Findings

Spreading velocity decreases logarithmically over time.

Initial spreading does not follow a pure power-law growth.

Contact line dissipation is negligible initially.

Abstract

Liquid drops start spreading directly after coming into contact with a solid sub- strate. Although this phenomenon involves a three-phase contact line, the spread- ing motion can be very fast. We experimentally study the initial spreading dy- namics, characterized by the radius of the wetted area, for viscous drops. Using high-speed imaging with synchronized bottom and side views gives access to 6 decades of time resolution. We show that short time spreading does not exhibit a pure power-law growth. Instead, we find a spreading velocity that decreases logarithmically in time, with a dynamics identical to that of coalescing viscous drops. Remarkably, the contact line dissipation and wetting effects turn out to be unimportant during the initial stages of drop spreading.