Coupling the Leidenfrost Effect and Elastic Deformations to Power Sustained Bouncing

TL;DR

This paper introduces the elastic Leidenfrost effect observed in soft hydrogel spheres, revealing how vaporization-induced bouncing can sustain motion through microscopic energy harvesting, with broad implications for soft material applications.

Contribution

It demonstrates a novel elastic Leidenfrost effect in soft solids, showing how vaporization and elastic deformations enable sustained bouncing and energy harvesting.

Findings

Hydrogel spheres bounce repeatedly for minutes on hot surfaces.

High-frequency microscopic gap dynamics facilitate energy transfer.

The effect enables new energy injection strategies into soft materials.

Abstract

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. Here we introduce a new phenomenon that occurs with vaporizable soft solids: the elastic Leidenfrost effect. By dropping hydrogel spheres onto hot surfaces we find 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. We show how these otherwise-hidden agitations constitute work cycles that harvest mechanical energy from the vapour and sustain the bouncing. Our findings unleash a powerful and widely applicable strategy for injecting mechanical energy into soft materials, with relevance to fields ranging from soft robotics and metamaterials to microfluidics and active matter.