From Bouncing to Floating: The Leidenfrost Effect with Hydrogel Spheres

Area of Science:

• Materials Science
• Fluid Dynamics
• Thermodynamics

Background:

• The Leidenfrost effect describes how liquids and solids levitate on a vapor layer above a hot surface.
• Vaporizable soft solids, like hydrogels, previously demonstrated elastic bouncing, not floating.
• Understanding hydrogel behavior on hot surfaces is crucial for advanced material applications.

Purpose of the Study:

• To investigate the floating capability of hydrogel spheres on hot surfaces.
• To identify the parameters controlling the transition from bouncing to floating.
• To develop a model explaining the floating mechanism and its relationship to hydrogel shape.

Main Methods:

• Carefully lowering hydrogel spheres towards a heated surface at controlled velocities.
• Varying surface temperature and approach velocity to observe different phenomena.
• Measuring gap geometry and developing a theoretical model for the floating regime.

Main Results:

• Hydrogel spheres can achieve a stable floating state, not just bouncing.
• The transition to floating is governed by approach velocity and temperature, similar to the dynamic Leidenfrost effect.
• Power-law scalings were observed for gap geometry in the floating regime, explained by a vaporization-shape coupling model.

Conclusions:

• Hydrogel spheres exhibit a controllable bounce-to-float transition on hot surfaces.
• The findings provide a new understanding of the Leidenfrost effect with soft, vaporizable materials.
• Hydrogels offer a promising platform for designing and controlling floating objects by manipulating their shape.