Behavior of chemically powered Janus colloids in lyotropic chromonic liquid crystal.

Platinum-coated Janus colloids exhibit self-propelled motion in aqueous solution via the catalytic decomposition of hydrogen peroxide. Here, we report their motion in a uniformly aligned nematic phase of lyotropic chromonic liquid crystal, disodium cromoglycate (DSCG). When active Janus colloids are placed in DSCG, we find that the anisotropy of the liquid crystal imposes a strong sense of direction to their motion; the Janus colloids tend to move parallel to the nematic director.

Directional Swimming of B. Subtilis Bacteria Near a Switchable Polar Surface.

The dynamics of swimming bacteria depend on the properties of their habitat media. Recently it is shown that the motion of swimming bacteria dispersed directly in a non-toxic water-based lyotropic chromonic liquid crystal can be controlled by the director field of the liquid crystal. Here, we investigate whether the macroscopic polar order of a ferroelectric nematic liquid crystal (N) can be recognized by bacteria B.

Microsecond electro-optic switching in the nematic phase of a ferroelectric nematic liquid crystal.

Nematic liquid crystals exhibit nanosecond electro-optic response to an applied electric field which modifies the degree of orientational order without realigning the molecular orientation. However, this nanosecond electrically modified order parameter (NEMOP) effect requires high driving fields, on the order of 10 V/m for a modest birefringence change of 0.01.

Dielectric Properties of a Ferroelectric Nematic Material: Quantitative Test of the Polarization-Capacitance Goldstone Mode.

The recently discovered ferroelectric nematic (N_{F}) liquid crystals (LC) have been reported to show an extraordinarily large value of the real part of the dielectric constant (ϵ^{'}>10^{3}) at low frequencies. However, it was argued by Clark et al. in Phys.

Trapping of isotropic droplets by disclinations in nematic liquid crystals controlled by surface anchoring and elastic constant disparity.

Linear defects such as dislocations and disclinations in ordered materials attract foreign particles since they replace strong elastic distortions at the defect cores. In this work, we explore the behavior of isotropic droplets nucleating at singular disclinations in a nematic liquid crystal, predesigned by surface photopatterning. Experiments show that in the biphasic nematic-isotropic region, although the droplets are attracted to the disclination cores, their centers of mass shift away from the core centers as the temperature increases.

Confinement and magnetic-field effect on chiral ferroelectric nematic liquid crystals in Grandjean-Cano wedge cells.

We explore the structure and magnetic-field response of edge dislocations in Grandjean-Cano wedge cells filled with chiral mixtures of the ferroelectric nematic mesogen DIO. Upon cooling, the ordering changes from paraelectric in the cholesteric phase N^{*} to antiferroelectric in the smectic SmZ_{A}^{*} and to ferroelectric in the cholesteric N_{F}^{*}. Dislocations of the Burgers vector b equal to the helicoidal pitch P are stable in all three phases, while dislocations with b=P/2 exist only in the N^{*} and SmZ_{A}^{*}.

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.

Chiral ground states of ferroelectric liquid crystals.

Ferroelectric nematic liquid crystals are formed by achiral molecules with large dipole moments. Their three-dimensional orientational order is described as unidirectionally polar. We demonstrate that the ground state of a flat slab of a ferroelectric nematic unconstrained by externally imposed alignment directions is chiral, with left- and right-handed twists of polarization.

Polar Self-Organization of Ferroelectric Nematic-Liquid-Crystal Molecules on Atomically Flat Au(111) Surface.

Understanding nanoscale mechanisms responsible for the recently discovered ferroelectric nematics can be helped by direct visualization of self-assembly of strongly polar molecules. Here, we report on scanning tunneling microscopy studies of monomolecular layers of a ferroelectric nematic liquid crystal on a reconstructed Au(111) surface. The monolayers are obtained by deposition from a solution at ambient conditions.

Topological transformations of a nematic drop.

Morphogenesis of living systems involves topological shape transformations which are highly unusual in the inanimate world. Here, we demonstrate that a droplet of a nematic liquid crystal changes its equilibrium shape from a simply connected tactoid, which is topologically equivalent to a sphere, to a torus, which is not simply connected. The topological shape transformation is caused by the interplay of nematic elastic constants, which facilitates splay and bend of molecular orientations in tactoids but hinders splay in the toroids.

Instantaneous mapping of liquid crystal orientation using a polychromatic polarizing microscope.

Polarizing microscopy brought about many advancements in the science of liquid crystals and other soft materials, including those of biological origin. Recent developments in optics and computer-based analysis enabled a new generation of quantitative polarizing microscopy which produces spatial maps of the optic axis. Unfortunately, most of the available approaches require a long acquisition time of multiple images which are then analyzed to produce the map.

Ferroelectric nematic liquids with conics.

Spontaneous electric polarization of solid ferroelectrics follows aligning directions of crystallographic axes. Domains of differently oriented polarization are separated by domain walls (DWs), which are predominantly flat and run along directions dictated by the bulk translational order and the sample surfaces. Here we explore DWs in a ferroelectric nematic (N) liquid crystal, which is a fluid with polar long-range orientational order but no crystallographic axes nor facets.

In situ measurements of twist and bend elastic constants in the oblique helicoidal cholesteric.

Unique electro-optical properties of the oblique helicoidal cholesteric (Ch_{OH}) stem from its heliconical director structure. An applied electric field preserves the single-harmonic modulation of the director while tuning the Ch_{OH} period and the corresponding Bragg-peak wavelength within a broad spectral range. We use the response of Ch_{OH} to the electric field to measure the elastic constants of twist K_{22} and bend K_{33} directly in the cholesteric phase.

Soliton walls paired by polar surface interactions in a ferroelectric nematic liquid crystal.

Surface interactions are responsible for many properties of condensed matter, ranging from crystal faceting to the kinetics of phase transitions. Usually, these interactions are polar along the normal to the interface and apolar within the interface. Here we demonstrate that polar in-plane surface interactions of a ferroelectric nematic N produce polar monodomains in micron-thin planar cells and stripes of an alternating electric polarization, separated by [Formula: see text] domain walls, in thicker slabs.

Combined electric and photocontrol of selective light reflection at an oblique helicoidal cholesteric liquid crystal doped with azoxybenzene derivative.

An oblique helicoidal cholesteric liquid crystal Ch_{OH} represents a unique optical material with a single-harmonic periodic modulation of the refractive index and a pitch that can be tuned by an electric or magnetic field in a broad range from submicrometers to micrometers. In this work, we demonstrate that the oblique helicoidal cholesteric doped with azoxybenzene molecules can be tuned by both the electric field and light irradiation. The tuning mechanism is explained by the kinetics of trans-cis photoisomerization of the azoxybenzene molecules.

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).

Elasticity and Viscosity of DNA Liquid Crystals.

Concentrated solutions of blunt-ended DNA oligomer duplexes self-assemble in living polymers and order into lyotropic nematic liquid crystal phase. Using the optical torque provided by three distinct illumination geometries, we induce independent splay, twist, and bend deformations of the DNA nematic and measure the corresponding elastic coefficients , , and , and viscosities η, η, and η. We find the viscoelasticity of the system to be remarkably soft, as the viscoelastic coefficients are smaller than in other lyotropic liquid crystals.

Topology control of human fibroblast cells monolayer by liquid crystal elastomer.

Eukaryotic cells in living tissues form dynamic patterns with spatially varying orientational order that affects important physiological processes such as apoptosis and cell migration. The challenge is how to impart a predesigned map of orientational order onto a growing tissue. Here, we demonstrate an approach to produce cell monolayers of human dermal fibroblasts with predesigned orientational patterns and topological defects using a photoaligned liquid crystal elastomer (LCE) that swells anisotropically in an aqueous medium.

Cell alignment by smectic liquid crystal elastomer coatings with nanogrooves.

Control of cells behavior through topography of substrates is an important theme in biomedical applications. Among many materials used as substrates, polymers show advantages since they can be tailored by chemical functionalization. Fabrication of polymer substrates with nano- and microscale topography requires processing by lithography, microprinting, etching, and so forth.

Design of nematic liquid crystals to control microscale dynamics.

The dynamics of small particles, both living such as swimming bacteria and inanimate, such as colloidal spheres, has fascinated scientists for centuries. If one could learn how to control and streamline their chaotic motion, that would open technological opportunities in the transformation of stored or environmental energy into systematic motion, with applications in micro-robotics, transport of matter, guided morphogenesis. This review presents an approach to command microscale dynamics by replacing an isotropic medium with a liquid crystal.

Laser-Induced Nanodroplet Injection and Reconfigurable Double Emulsions with Designed Inner Structures.

Microfabrication of complex double emulsion droplets with controlled substructures, which resemble biological cells, is an important but a highly challenging subject. Here, a new approach is proposed based on laser-induced injection of water nanodroplets into a liquid crystal (LC) drop. In contrast to the conventional top-down microfluidic fabrication, this method employs a series of bottom-up strategies such as nanodroplet injection, spontaneous and assisted coalescence, elastically driven actuation, and self-assembly.