Viscoelasticity and elastocapillarity effects in the impact of drops on a repellent surface

TL;DR

This study explores how viscoelastic and elastocapillary effects influence the impact dynamics of drops on super-repellent surfaces, using high-speed imaging and a harmonic oscillator model to analyze maximal expansion and timing.

Contribution

It introduces a comprehensive experimental and theoretical analysis of viscoelastic drop impacts, highlighting the roles of elasticity, capillarity, and viscous dissipation in the dynamics.

Findings

The generalized damped harmonic oscillator model accurately predicts impact dynamics.

Viscoelastic properties significantly affect maximal expansion and impact timing.

Capillarity and elasticity interplay influences the impact behavior of non-Newtonian fluids.

Abstract

We investigate freely expanding viscoelastic sheets. The sheets are produced by the impact of drops on a quartz plate covered with a thin layer of liquid nitrogen that suppresses shear viscous dissipation as a result of the cold Leidenfrost effect. The time evolution of the sheet is simultaneously recorded from top and side views using high-speed cameras. The investigated viscoelastic fluids are Maxwell fluids, which are characterized by low elastic moduli, and relaxation times that vary over almost two orders of magnitude, thus giving access to a large spectrum of viscoelastic and elastocapillary effects. For the purposes of comparison, Newtonian fluids, with viscosity varying over three orders of magnitude, are also investigated. In this study, $d_{\mathrm{max}}$, the maximal expansion of the sheets, and $t_{\mathrm{max}}$ the time to reach this maximal expansion from the time at impact, are measured as a function of the impact velocity. By using a generalized damped harmonic oscillator model, we rationalize the role of capillarity, bulk elasticity and viscous dissipation in the expansion dynamics of all investigated samples. In the model, the spring constant is a combination of the surface tension and the bulk dynamic elastic modulus. The time-varying damping coefficient is associated to biaxial extensional viscous dissipation and is proportional to the dynamic loss modulus. For all samples, we find that the model reproduces accurately the experimental data for $d_{\mathrm{max}}$ and $t_{\mathrm{max}}$.