Instabilities and Flow-induced Structures in Nematic Liquid Crystals

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.

Bio: Irmgard Bischofberger is an experimentalist working in the fields of fluid dynamics and soft condensed matter. She obtained her Ph.D. degree in Physics from the University of Fribourg (Switzerland) and has been a postdoctoral fellow in the Physics Department at the University of Chicago. She is currently an associate professor in the Department of Mechanical Engineering at MIT. Her research interests include the spontaneous pattern formation from fluid instabilities and drying processes and non-equilibrium phenomena in colloidal gels.

All seminars are held on Wednesdays from 12:00 noon-1:00 p.m. in the Bowen Hall Auditorium Room 222. A light lunch is provided at 11:30 a.m. in the Bowen Hall Atrium immediately prior to the seminar.