When elasticity affects drop coalescence

TL;DR

This paper investigates how polymer elasticity influences drop coalescence, revealing an elastic singularity with diverging curvature and showing that polymers affect spatial features but not the temporal evolution of the coalescence process.

Contribution

It introduces a novel viscoelastic similarity analysis to explain how elasticity impacts drop coalescence, highlighting the emergence of an elastic singularity.

Findings

Elastic singularity characterized by diverging interface curvature.

Polymers influence spatial features but not the temporal evolution of coalescence.

Relevance to biofluids, coating sprays, and inkjet printing.

Abstract

The breakup and coalescence of drops are elementary topological transitions in interfacial flows. The breakup of a drop changes dramatically when polymers are added to the fluid. With the strong elongation of the polymers during the process, long threads connecting the two droplets appear prior to their eventual pinch-off. Here, we demonstrate how elasticity affects drop coalescence, the complement of the much studied drop pinch-off. We reveal the emergence of an elastic singularity, characterised by a diverging interface curvature at the point of coalescence. Intriguingly, while the polymers dictate the \emph{spatial} features of coalescence, they hardly affect the \emph{temporal} evolution of the bridge. These results are explained using a novel viscoelastic similarity analysis and are relevant for drops created in biofluids, coating sprays and inkjet printing.