Using the Leidenfrost effect and hot hydrogels to make better bouncy balls
Par Scott Waitukaitis, Universiteit Leiden / AMOLF, Amsterdam, The Netherlands
Mardi 05 Décembre, 14h, Salle des séminaires (215), 2ème étage, Bâtiment A4N
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, nothing is known about the effect with materials whose stiffness lies between these extremes. In this talk, I will introduce a new phenomenon that occurs with vaporizable soft solids: the elastic Leidenfrost effect. By dropping hydrogel spheres onto hot surfaces we see that, rather than hovering, they harvest energy from their interaction with the surface and energetically bounce several times their diameter for minutes at a time. With high-speed video during a single impact, we uncover high-frequency microscopic gap dynamics at the sphere-substrate interface. These otherwise-hidden agitations constitute work cycles that siphon energy from the vapour and sustain the bouncing. The findings unleash a widely applicable strategy for injecting mechanical energy into soft materials, with potential relevance to fields ranging from soft robotics and metamaterials to microfluidics and active matter.