Laboratoire Matière et Systèmes Complexes

Impact of drops and balls : Spread, Bounce or Burst of Soft Matter sheets

Prof. Christian LIGOURE Laboratoire Charles Coulomb UMR 5221CNRS-UM Université de Montpellier

In a first part I will focus on the destabilization of dilute oil-in-water emulsion-based liquid sheets expanding in air. A sheet results from the collision of a single tear on a small solid target ; it disintegrates through the nucleation and growth of holes that perforate the sheet. We have developed an optical technique that allows the determination of the time and space-resolved thickness of the sheet to gain a, understanding of the physical mechanisms f the perforation events This bursting based-liquid sheet destabilization is at the origin of emulsion-based anti-drift formulations are developed for agricultural spray.

In a second part, I will investigate freely expanding sheets formed by ultra soft spherical gel beads of elastic but also liquid droplets with various surface tensions, and simple viscoelastic fluids (Maxwell fluids), produced by impacting them on a silicon wafer covered with a thin layer of liquid nitrogen that suppresses viscous dissipation by an inverse Leidenfrost effect.

The experiments reveal a universal behaviour of the impact dynamics with impact velocity, for both solids and liquids, and even viscoelastic fluids, that we have rationalized .