Grand Séminaire d'Institut

Vendredi 13 Octobre 2017 à 11h00.

Using the Leidenfrost effect and hot hydrogels to make better bouncy balls

''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 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 harvest mechanical 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. REF: Waitukaitis et al. Nature Physics (2017)''