Paper Number
IN6 

Session
Flow-induced Instabilities in Non-Newtonian Fluids

Title
Chiral domains in a flowing achiral nematic liquid crystal

Presentation Date and Time
October 11, 2022 (Tuesday) 5:25

Track / Room
Track 5 / Sheraton 2

Authors (Click on name to view author profile)

1. Zhang, Qing (MIT)
2. Zhang, Rui (Hong Kong University of Science and Technology)
3. Bischofberger, Irmgard (MIT)

Author and Affiliation Lines (in printed abstract book)
Qing Zhang¹, Rui Zhang² and Irmgard Bischofberger^1
1MIT, Cambridge, MA; ²Hong Kong University of Science and Technology, Hong Kong, Hong Kong

Speaker / Presenter 
Bischofberger, Irmgard

Keywords
flow-induced instabilities

Text of Abstract
An achiral nematic liquid in a microfluidic cell could be expected to form achiral structures in a pressure-driven flow. Surprisingly, we find the spontaneous emergence of chiral structures when an achiral lyotropic chromonic liquid crystal in the nematic phase relaxes from a high velocity flow to a steady-state lower velocity flow. The chirality results from a periodic double-twist deformation of the liquid crystal and leads to striking stripe patterns vertical to the flow direction. We show that the double-twist deformation is triggered at regions of biaxial-splay deformations that become unstable. The transition from these biaxial-splay deformations to the double-twist deformations can be rationalized by the low Frank elastic energy stored in double-twist deformations compared to that stored in biaxial-splay deformations. We demonstrate that the period of the chiral structures can be tuned by the local flow velocity and is set by the competition between the bend elastic torque and the viscous torque acting on the structures.