Abstract

Active cholesterics are chiral in both their structure, which has continuous screw symmetry, and their active stresses, which include contributions from torque dipoles. Both expressions of chirality give rise to curl forces in the hydrodynamics, which we derive from the active Ericksen-Leslie equations using a geometric approach. This clarifies the hydrodynamics of continuous screw symmetry and provides an example of generalised odd elastic forces that originate from an equilibrium free energy. For the active instability, screw symmetry generates a contribution of chiral activity to the linearised pseudolayer hydrodynamics that is absent in materials with chiral activity but achiral structure and produces an active instability that is sensitive to the cholesteric handedness. Finally, as time allows, I will discuss the chiral hydrodynamics of materials with three-dimensional screw symmetry. This is joint work with SJ Kole, Ananyo Maitra and Sriram Ramaswamy.