Seminar Gulliver, Scott Waitukaitis (AMOLF and IST Austria)

4 février 11:30 » 12:30 — Bibliothèque PCT - F3.04

The Leidenfrost Effect and Hydrogels

The Leidenfrost effect occurs when an object near a hot surface vaporizes rapidly enough to lift itself up and hover. Although well-understood for liquids and stiff sublimable solids, little is known about the interaction of vaporizable soft solids with superheated surfaces. In this talk, I will introduce a new phenomenon that occurs with vaporizable soft solids : the elastic Leidenfrost effect. By dropping vaporizable hydrogel spheres onto hot surfaces I will show that, rather than hovering, they energetically bounce several times their diameter for minutes at a time. With high-speed video during a single impact, one sees high-frequency microscopic gap dynamics at the sphere-substrate interface. Solving for the dynamics of a simplified system with a simple numerical model, I will reveal how these otherwise-hidden agitations constitute work cycles that harvest mechanical energy from the vapor and sustain the bouncing. Finally, I will show that hydrogels are also capable of exhibiting the regular Leidenfrost effect, and that the transition between these two behaviors is controlled by the substrate temperature and impact velocity.

Haut de page