Brownian Dynamics of Particles “Dressed” by Chiral Director Configurations in Lyotropic Chromonic Liquid Crystals

We employ video microscopy to study the Brownian dynamics of colloidal particles suspended in the uniaxially aligned nematic phase of a lyotropic chromonic liquid crystal (LCLC), Disodium Cromoglycate (DSCG). DSCG is water soluble, and its nematic phase is characterized by an unusually large elastic anisotropy. Our measurements of the mean-square displacement for polystyrene-based colloidal microspheres show sub-diffusive behaviors along directions parallel and perpendicular to the nematic director. The dynamics parallel to the far-field director is sub-diffusive for lag times as long as several seconds and then diffusive beyond that, while the dynamics perpendicular to the far-field director continues to display complicated and unexpected sub-diffusive behavior for hundreds of seconds of lag time. Also, spherical colloids suspended in LCLCs can induce two symmetrically and energetically distinct director field configurations and we consider the effects of these differences on the diffusion dynamics of LCLC colloids. The origin of these deviations from conventional diffusion theory are discussed and our results are compared to previous diffusion experiments in conventional nematic liquid crystals.