High-Order Nonlinear Electrophoresis in a Nematic Liquid Crystal.

Electrophoresis is the motion of particles relative to a surrounding fluid driven by a uniform electric field. In conventional electrophoresis, the electrophoretic velocity grows linearly with the applied field. Nonlinear effects with a quadratic speed vs field dependence are gaining research interest since an alternating current field could drive them. Here, we report on the giant nonlinearity of electrophoresis in a nematic liquid crystal in which the speed grows with the fourth and sixth powers of the electric field. The mechanism is attributed to the shear thinning of the nematic environment induced by the moving colloid. The observed giant nonlinear effect dramatically enhances the efficiency of electrophoretic transport.

Correction: Shear-induced polydomain structures of nematic lyotropic chromonic liquid crystal disodium cromoglycate.

Correction for 'Shear-induced polydomain structures of nematic lyotropic chromonic liquid crystal disodium cromoglycate' by Hend Baza et al., Soft Matter, 2020, 16, 8565-8576.

Shear-induced polydomain structures of nematic lyotropic chromonic liquid crystal disodium cromoglycate.

Lyotropic chromonic liquid crystals (LCLCs) represent aqueous dispersions of organic disk-like molecules that form cylindrical aggregates. Despite the growing interest in these materials, their flow behavior is poorly understood. Here, we explore the effect of shear on dynamic structures of the nematic LCLC, formed by 14 wt% water dispersion of disodium cromoglycate (DSCG). We employ in situ polarizing optical microscopy (POM) and small-angle and wide-angle X-ray scattering (SAXS/WAXS) to obtain independent and complementary information on the director structures over a wide range of shear rates. The DSCG nematic shows a shear-thinning behavior with two shear-thinning regions (Region I at [small gamma, Greek, dot above] < 1 s-1 and Region III at [small gamma, Greek, dot above] > 10 s-1) separated by a pseudo-Newtonian Region II (1 s-1 < [small gamma, Greek, dot above] < 10 s-1). The material is of a tumbling type. In Region I, [small gamma, Greek, dot above] < 1 s-1, the director realigns along the vorticity axis. An increase of [small gamma, Greek, dot above] above 1 s-1 triggers nucleation of disclination loops. The disclinations introduce patches of the director that deviates from the vorticity direction and form a polydomain texture. Extension of the domains along the flow and along the vorticity direction decreases with the increase of the shear rate to 10 s-1. Above 10 s-1, the domains begin to elongate along the flow. At [small gamma, Greek, dot above] > 100 s-1, the texture evolves into periodic stripes in which the director is predominantly along the flow with left and right tilts. The period of stripes decreases with an increase of [small gamma, Greek, dot above]. The shear-induced transformations are explained by the balance of the elastic and viscous energies. In particular, nucleation of disclinations is associated with an increase of the elastic energy at the walls separating nonsingular domains with different director tilts. The uncovered shear-induced structural effects would be of importance in the further development of LCLC applications.