Elastic Rayleigh-Plateau instability: Dynamical selection of nonlinear states

TL;DR

This paper investigates the nonlinear surface instability of elastic hydrogel threads, revealing how capillarity and elasticity compete to select final morphologies through a combination of analysis, simulations, and experiments.

Contribution

It introduces a phase map of possible shapes for elastic cylinders under capillary forces and explains the dynamical selection of patterns.

Findings

Identification of coexistence of cylinders-on-a-string and beads-on-a-string configurations.

Determination of the characteristic wavelength of selected patterns.

Validation of slender analysis results with simulations and experiments.

Abstract

A slender thread of elastic hydrogel is susceptible to a surface instability that is reminiscent of the classical Rayleigh-Plateau instability of liquid jets. The final, highly nonlinear states that are observed in experiments arise from a competition between capillarity and large elastic deformations. Combining a slender analysis and fully three-dimensional numerical simulations, we present the phase map of all possible morphologies for an unstable neo-Hookean cylinder subjected to capillary forces. Interestingly, for softer cylinders we find the coexistence of two distinct configurations, namely, cylinders-on-a-string and beads-on-a-string. It is shown that for a given set of parameters, the final pattern is selected via a dynamical evolution. To capture this, we compute the dispersion relation and determine the characteristic wavelength of the dynamically selected profiles. The validity of the "slender" results is confirmed via simulations and these results are consistent with experiments on elastic and viscoelastic threads.