Capillary Slinky: Equilibrium and Dynamics of Droplets in a Soft Spring

TL;DR

This paper investigates how liquid droplets interact with soft springs, revealing their equilibrium shapes, dynamic behaviors, and potential for actuation and flow control in soft elastic systems.

Contribution

It introduces experimental insights into droplet shapes and flows in soft springs, demonstrating surface tension's role in actuation and active flow control.

Findings

Droplets form annulus, Eruciform, and spherical shapes in soft springs.

Different flow regimes with significant internal rotational flow observed.

Surface tension can actuate springs by stretching and compression.

Abstract

Springs can be found in many applications and biological systems, and when these are soft, they easily deform. At small scales, capillarity can induce a force leading to spring deformations when the elastocapillary number is small. We demonstrate through experiments the non-trivial equilibrium shape liquid droplets adopt in these soft springs, which form an annulus, Eruciform, and spherical shapes. When these droplets are set in motion, they display different flow regimes with significant dissipation generated by the internal rotational flow. The static and dynamics of droplets in such a capillary slinky is also used to demonstrate how surface tension can actuate springs by stretching/compression, while providing a way for active flow control in soft springs.