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Capillary slinky: Equilibrium and dynamics of a droplet in a soft spring

Bidisha Bhatt1 and Andreas Carlson1,2,*

  • *Contact author: acarlson@math.uio.no
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Phys. Rev. Fluids 11, 043607 – Published 29 April, 2026

DOI: https://doi.org/10.1103/p9j4-hp5h

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 nontrivial 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 are also used to demonstrate how surface tension can actuate springs by stretching/compression, while providing a way for active flow control in soft springs.

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Phys. Rev. Fluids 11, 043607– Published 29 April, 2026
  • Received 14 January 2026
  • Accepted 6 March 2026
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