Tunable Thin Elasto-Drops

TL;DR

This paper introduces a method to create and study elastic capsules with tunable thickness and surface tension, serving as macroscopic analogues of liquid drops for elastic and fluid dynamics research.

Contribution

The authors develop a fabrication and analysis technique for elastic capsules that act as large-scale elasto-drops with adjustable surface tension and negligible bending stiffness.

Findings

Capsules' hoop stress can be accurately measured via surface wave analysis.

Capsules behave as elastic analogues of liquid drops with tunable surface tension.

Bending stiffness is negligible at relevant wavelengths, simplifying the shell dynamics.

Abstract

We present an experimental method to fabricate centimetric thin elastic capsules with highly uniform thickness and negligible bending stiffness using silicone elastomers. In our experiments, the capsules thickness is tunable at fabrication, while internal pressure and hoop (circumferential) stress are adjustable via hydrostatic inflation once the capsules are filled and immersed in water. Capsules mechanics are probed through hydro-elastic waves generated by weak mechanical perturbations at the capsule interface. By analyzing the surface wave dynamics in the Fourier domain, we extract the in-plane stress and demonstrate that the hydro-elastic waves are exclusively governed by hoop stress. This \reponse{provides a controllable macroscopic analogue of liquid drops} characterised by an effective surface tension, allowing the capsules to be modeled as large-scale ``elasto-drops'' with an inflation and thickness tunable effective surface tension. \reponse{In this limit, bending stiffness is negligible over the experimentally relevant wavelengths, so that the shell dynamics are governed primarily by in-plane tension.} Our work demonstrates that elasto-drops serve as a robust model system for parametric studies of large-scale \reponse{analogues of} liquid drops with experimentally adjustable surface tension.