Pretransitional fluctuations in the isotropic phase of a lyotropic chromonic liquid crystal

Abstract

We have studied isotropic-to-nematic pretransitional fluctuations in an aqueous solution of disodium cromoglycate (cromolyn) by static and dynamic light scattering. Cromolyn is a representative of lyotropic chromonic liquid crystals with building units being elongated rods formed by aggregates of disk-like molecules. By combining light-scattering and viscosity measurements we have determined the correlation length and relaxation time of the orientational order-parameter fluctuations and estimated the size of the cromolyn aggregates. The pretransitional behavior of light scattering does not completely follow the classic Landau-de Gennes model. This feature is most probably associated with the variable length of cromolyn aggregates. We have observed a dramatic increase of the shear viscosity near the transition to the nematic phase, the fact which correlates with the idea of growing supramolecular aggregates. The steep temperature dependence of the viscosity is accompanied by a practically temperature-independent translational diffusion coefficient.

Elasticity, viscosity, and orientational fluctuations of a lyotropic chromonic nematic liquid crystal disodium cromoglycate

“…L z 25 nm, which compares well with a previous estimate 58 L ¼ 18 nm for the isotropic phase of the same concentration at 305 K (5 K above T ni ).…”

Tunable depletion potentials driven by shape variation of surfactant micelles

“…Ultimately, the experimenter will generate strong evidence "for" or "against" each microscopic model from which a microscopic understanding of the local micro-and nanoenvironment around the particles can be deduced. One interesting new opportunity is to study depletion due to lyotropic chromonic liquid crystals [83][84][85][86] wherein the underlying plank-like macromolecules stack to produce rod-like mesogens which in turn assemble into liquid crystalline phases; the present method offers a novel way to measure the average length and length distribution of the stacks. In principle, the measurement also offers a tool to probe the size, shape, and folding of proteins.…”

Thermophysical Properties of Fluids and Fluid Mixtures

“…In addition to studying polymer solutions and aqueous electrolyte solutions we have investigated critical fluctuations in liquid crystals [22,76], crossover kinetics of asphaltene aggregation in hydrocarbon solutions [24], and dynamics of gel formation andbreakage in a biopolymer gel [66]. We have elucidated the nature of the mysterious blue-phase-111-isotropic critical point in a chiral liquid crystalline solution and shown that this critical point belongs to the same universality class as ordinary critical points in fluids [22].…”

“…By combining lightscattering and viscosity measurements we have determined the correlation length and relaxation time of the orientational order-parameter fluctuations and shown that the pretransitional fluctuations are accompanied by elongation of the cromolyn aggregates [76].…”