Mechanical and Civil Engineering Seminar

Abstract: 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 pure twist disclination loops and, surprisingly, to the spontaneous emergence of chiral domains at low shear rates.

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 assistant 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.