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.Graphical abstract
Highlights
Introduction and phenomenologyChirality is ubiquitous in Nature, from the helical structure of DNA [23], to bacterial flagella and their rotary motors [24, 25], to selective reflection and structural colour in both plants and animals [26,27]
We provide a detailed comparison between active cholesterics and the behaviour already established for active nematic and smectic phases
It is for this reason that the instability of active cholesterics occurs for extensile materials, in contrast to the situation in active smectics, where it is the contractile material that is unstable [19]
Summary
Chirality is ubiquitous in Nature, from the helical structure of DNA [23], to bacterial flagella and their rotary motors [24, 25], to selective reflection and structural colour in both plants and animals [26,27]. Such distortions and flows arise most in response to a uniform conical tilt of the cholesteric director into the pitch direction This situation can be described in a quasi–onedimensional setting identical to that studied extensively in the context of spontaneous flow transitions in active nematics [65] and polar gels [66]. In this sense it may be considered the natural cholesteric analogue of those studies and the analysis is broadly the same, the structure of the director distortions and flows are markedly different, again emphasising the contrasting character of active cholesterics compared to other forms of active matter. This ordered state is destroyed at larger activity with a transition to a state of active turbulence
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
