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.

17 pages, 9 figures

References in corpus (9)

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Cited by in corpus (19)

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• Active matter
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• Design of nematic liquid crystals to control microscale dynamics
• Oriented Active Solids
• Topology of three-dimensional active nematic turbulence confined to droplets
• Active cholesterics: odder than odd elasticity
• Topological states in chiral active matter: dynamic blue phases and active half-skyrmions
• Helfrich-Hurault elastic instabilities driven by geometrical frustration
• Contact Topology and the Structure and Dynamics of Cholesterics
• Geometry of Bend: Singular Lines and Defects in Twist-Bend Nematics
• Chirality, anisotropic viscosity and elastic anisotropy in three-dimensional active nematic turbulence
• Active Nematic Multipoles: Flow Responses and the Dynamics of Defects and Colloids
• Chirality and odd mechanics in active columnar phases
• Long-wavelength instabilities in a system of interacting active particles
• Simulations of Three-dimensional Nematic Guidance of Microswimmers
• Screw Symmetry, Chiral Hydrodynamics and Odd Instability in Active Cholesterics