Symmetrically pulsating bubbles swim in an anisotropic fluid by nematodynamics

TL;DR

This paper demonstrates that pulsating spherical bubbles can swim in nematic liquid crystals due to anisotropic fluid properties and symmetry breaking, revealing a new propulsion mechanism in complex fluids.

Contribution

The study introduces a novel mechanism where anisotropic nematic fluids enable symmetric pulsating bubbles to swim, highlighting the role of nematodynamics and topological defects.

Findings

Bubbles swim despite centrosymmetry due to nematic director deformation.

Speed is enhanced by confinement effects.

Propulsion observed in symmetry-broken bubbles with disclinations.

Abstract

Swimming in low-Reynolds-number fluids requires the breaking of time-reversal symmetry and centrosymmetry. Microswimmers, often with asymmetric shapes, exhibit nonreciprocal motions or exploit nonequilibrium processes to propel. The role of surrounding fluids has also attracted attention because viscoelastic, non-Newtonian, and anisotropic properties of fluids matter in propulsion efficiency and navigation. Here we experimentally demonstrate that anisotropic fluids, nematic liquid crystals (NLC), can make a pulsating spherical bubble swim despite its centrosymmetric shape and time-symmetric motion. The NLC breaks the centrosymmetry by a deformed nematic director field with a topological defect accompanying the bubble. The nematodynamics renders the nonreciprocity in the pulsation-induced fluid flow. We also report the speed enhancement by confinement and the propulsion of another symmetry-broken bubble dressed by a bent disclination. Our experiments and theory elucidate another possible mechanism of moving bodies in complex fluids by spatiotemporal symmetry breaking.