Maximal spreading of impacting viscoelastic droplets

TL;DR

This study investigates how viscoelasticity influences the maximum spreading of impacting droplets, revealing significant reductions in spreading diameter at certain conditions through experiments and modeling.

Contribution

It introduces a new understanding of viscoelastic effects on droplet impact dynamics by combining experiments with an energy balance model.

Findings

Viscoelastic droplets show reduced maximal spreading compared to Newtonian ones.

The reduction is significant when the Deborah number is around unity.

A scaling model explains the influence of fluid properties on spreading behavior.

Abstract

Droplet impact and spreading on solid substrates are well understood for Newtonian fluids, yet how viscoelasticity alone modifies the maximal spreading remains unclear. To identify the mechanisms governing the spreading dynamics, we conducted impact experiments and measured the maximal spreading diameter to quantify how fluid elasticity modifies the maximal spreading of impacting droplets. Experiments were performed using fluids within a narrow range of viscosity and surface tension, but with varying relaxation times. For a wide range of conditions, viscoelastic droplets follow a similar behavior as Newtonian ones; however, their maximal spreading diameter is significantly reduced compared with the Newtonian behavior when the Deborah number is of order unity. These observations are rationalized by incorporating the viscoelastic effects into a classical energy balance model. The scaling argument obtained from this model explains the reported reduction in maximal spreading and identifies the range of fluid properties for which the strongest viscoelastic effects emerge.