Supramolecular chirality typically originates from either chiral molecular building blocks or external chiral stimuli. Generating chirality in achiral systems in the absence of a chiral input, however, is non-trivial and necessitates spontaneous mirror symmetry breaking. Achiral nematic lyotropic chromonic liquid crystals have been reported to break mirror symmetry under strong surface or geometric constraints. Here we describe a previously unrecognised mechanism for creating chiral structures by subjecting the material to a pressure-driven flow in a microfluidic cell. The chirality arises from a periodic double-twist configuration of the liquid crystal and manifests as a striking stripe pattern. We show that the mirror symmetry breaking is triggered at regions of flow-induced biaxial-splay configurations of the director field, which are unstable to small perturbations and evolve into lower energy structures. The simplicity of this unique pathway to mirror symmetry breaking can shed light on the requirements for forming macroscopic chiral structures.

The codes and data in this project are all included. Data both in main text and SI are included into the data.zip file. Source_Data.xlsx includes all the data except Fig.S8. Fig.S8 can be viewed by Fig_S8.psvm through Paraview. When loading Fig_S8.psvm through paraview, choose "Search files under specified directory", and then choose the downloaded 'data' file. Codes used in this study are all included in the script.zip file. crossed_polarizer inculdes the C script which can generate the crossed polarizer image from simulated director field. Ericksen_Leslie analysis is included in the Ericksen_Leslie file. For further inquiries or issue reporting, you may contact us via email. Contact information: Qing Zhang (zqing@mit.edu) Irmgard Bischofberger (irmgard@mit.edu) Rui Zhang (ruizhang@ust.hk) Weiqiang Wang (wwangch@connect.ust.hk)