Lyotropic chromonic liquid crystals in the nematic phase are anisotropic fluids. We exploit this intrinsic anisotropy to probe growth morphology transitions that occur in the viscous-fingering instability upon the displacement of the liquid crystal by a less-viscous Newtonian liquid. In isotropic systems, this instability produces complex patterns that are characterized by repeated branching of the evolving structure, which leads to the common morphologies of fractal or dense-branching growth. In anisotropic systems, by contrast, the growth morphology changes to dendritic growth characterized by stable needle-like structures. We show that the morphology transition coincides with the onset of shear-alignment at high shear rates, where the shear forces become dominant over the elastic forces from the nematogenic potential. Below this critical shear rate, the lyotropic chromonic liquid crystal exhibits a tumbling behavior that leads to the formation of novel types of defects and flow structures, including the surprising emergence of chiral domains despite the achiral nature of the material.
About the Speaker
Irmgard Bischofberger is an Assistant Professor in the Department of Mechanical Engineering at MIT. She obtained her Ph.D. degree in Physics from the University of Fribourg (Switzerland) and was a postdoctoral fellow at the University of Chicago. Irmgard is an experimentalist working in the fields of fluid dynamics and soft condensed matter. Her research interests include the spontaneous pattern formation from fluid instabilities and drying processes and non-equilibrium phenomena in soft gels. Irmgard is passionate about communicating science to a diverse audience and has a longstanding ‘Science and Arts’ collaboration with artists and musicians.