Instabilities and flow-induced structures in nematic liquid crystals

Instabilities and flow-induced structures in nematic liquid crystals
Irmgard Bischofberger, MIT, Department of Mechanical Engineering
Irmgard Bischofberger
Date and time: Thu, Dec 01, 2022 - 11:30am
Refreshments at 11:15am
Location: LGRT 1033
Category: Condensed Matter Seminar
Abstract:

Lyotropic chromonic liquid crystal (LCLC) solutions in the nematic phase have peculiar properties. They are tumbling materials, which means that flows can easily destabilize the director alignment, and they possess a large elastic anisotropy where twist elastic deformations are energetically much cheaper than splay or bend deformations. We show how these characteristics can be exploited to induce controlled growth morphology transitions from the generic dense-branching growth to dendritic growth in the viscous-fingering instability, and how they lead to unique structure formation as the LCLC solutions are driven out-of-equilibrium by a pressure-driven flow in a microfluidic channel. In particular, we report the surprising emergence of chiral domains in the material despite the achiral nature of the material. 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 discuss the mechanism of this unique pathway to spontaneous mirror symmetry breaking and rationalize the selection of a well-defined period of the chiral domains.