Taras Turiv

Shear-aligned living liquid crystals exhibit a cascade of bend instabilities followed by defect nucleation and proliferation after shear cessation.

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.

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 < 1 s⁻¹ and Region III at > 10 s⁻¹) separated by a pseudo-Newtonian Region II (1 s⁻¹ < < 10 s⁻¹). The material is of a tumbling type. In Region I, < 1 s⁻¹, the director realigns along the vorticity axis. An increase of 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 > 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 . 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.

Photopatterned liquid crystal elastomer templates living tissue with predesigned alignment patterns and topological defects.

Biological cells in living tissues form dynamic patterns with local orientational order and topological defects. Here we demonstrate an approach to produce cell monolayer with the predesigned orientational patterns using human dermal fibroblast cells (HDF) placed onto a photoaligned liquid crystal elastomer (LCE). The alignment of cells is caused by anisotropic swelling of the substrates in contact with the aqueous cell growth medium. The patterns predesigned in the LCE cause a strong spatial variation of cell phenotype (evidenced by shape variations), their surface density and number density fluctuations. The concentration of cells is significantly higher near the cores of positive-strength defects as compared to negative-strength defects. Unbinding of defect pairs intrinsic to active matter is suppressed by anisotropic surface anchoring. The geometry of arrays allows one to estimate the elastic and surface anchoring characteristics of the tissues. The demonstrated patterned LCE approach could be used to control the collective behavior of cells in living tissues, cell differentiation, and tissue morphogenesis.

We report dynamic light scattering measurements of the orientational (Frank) elastic constants and associated viscosities among a homologous series of a liquid crystalline dimer, trimer, and tetramer exhibiting a uniaxial nematic (N) to twist-bend nematic (N_TB) phase transition.

The original version of this article contained an error in the description of Supplementary Movie 7, which incorrectly read ‘Collision resulting in annihilation of two solitons. U = 45.1 V, f = 600 Hz, T = 50 °C, d = 8.0 μm. The original movie is taken at the frame rate of 91 fps. The playback speed is 7 fps.’ The correct version reads ‘Death of a soliton at a dust particle. U = 65.6 V, f = 800 Hz, T = 50 °C, d = 7.7 µm. The original movie is taken at the frame rate of 92 fps. The playback speed is 7 fps.’ The HTML has been updated to include a corrected version of the ‘Description of Additional Supplementary Files’ file.