Hydrodynamic instabilities in active cholesteric liquid crystals

Abstract

We describe the basic properties and consequences of introducing active stresses, with principal direction along the local director, in cholesteric liquid crystals. The helical ground state is found to be linearly unstable to extensile stresses, without threshold in the limit of infinite system size, whereas contractile stresses are hydrodynamically screened by the cholesteric elasticity to give a finite threshold. This is confirmed numerically and the non-linear consequences of instability, in both extensile and contractile cases, are studied. We also consider the stresses associated to defects in the cholesteric pitch ($\lambda$ lines) and show how the geometry near to the defect generates threshold-less flows reminiscent of those for defects in active nematics. At large extensile activity $\lambda$ lines are spontaneously created and can form steady state patterns sustained by constant active flows.

arXiv comment17 pages, 9 figures

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Cited by in corpus (19)

• Topological active matter
• Active matter
• Rotation and propulsion in 3d active chiral droplets
• Topological defects in solids with odd elasticity
• Three-Dimensional Active Defect Loops
• Design of nematic liquid crystals to control microscale dynamics
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• Screw Symmetry, Chiral Hydrodynamics and Odd Instability in Active Cholesterics