# Drop-on-coilable-fibre systems exhibit negative stiffness events and transitions in coiling morphology

## TL;DR

This paper explores the unique mechanical behaviors of drop-on-coilable-fibre systems, revealing negative stiffness events and morphological transitions driven by capillary and elastic interactions through theoretical, numerical, and experimental methods.

## Contribution

It provides the first comprehensive analysis of negative stiffness phenomena and coiling morphology transitions in elastic fibres with liquid droplets, combining theory, simulations, and experiments.

## Key findings

- Identification of negative stiffness regimes linked to capillary energy transfer
- Observation of coiling morphology transitions under different mechanical conditions
- Coiling becomes an ordered phase with coexisting liquid and solid deformations

## Abstract

We investigate the mechanics of elastic fibres carrying liquid droplets. In such systems, buckling may localize inside the drop cavity if the fibre is thin enough. This so-called drop-on-coilable-fibre system exhibits a surprising liquid-like response under compression, and a solid-like response under tension. Here we analyze this unconventional behavior in further details and find theoretical, numerical and experimental evidences of negative stiffness events. We find that the first and main negative stiffness regime owes its existence to the transfer of capillary-stored energy into mechanical curvature energy. The following negative stiffness events are associated with changes in the coiling morphology of the fibre. Eventually coiling becomes tightly locked into an ordered phase where liquid and solid deformations coexist.