Showing papers on "Liquid crystal published in 2020"

Nature-Inspired Emerging Chiral Liquid Crystal Nanostructures: From Molecular Self-Assembly to DNA Mesophase and Nanocolloids.

Abstract: Liquid crystals (LCs) are omnipresent in living matter, whose chirality is an elegant and distinct feature in certain plant tissues, the cuticles of crabs, beetles, arthropods, and beyond. Taking inspiration from nature, researchers have recently devoted extensive efforts toward developing chiral liquid crystalline materials with self-organized nanostructures and exploring their potential applications in diverse fields ranging from dynamic photonics to energy and safety issues. In this review, an account on the state of the art of emerging chiral liquid crystalline nanostructured materials and their technological applications is provided. First, an overview on the significance of chiral liquid crystalline architectures in various living systems is given. Then, the recent significant progress in different chiral liquid crystalline systems including thermotropic LCs (cholesteric LCs, cubic blue phases, achiral bent-core LCs, etc.) and lyotropic LCs (DNA LCs, nanocellulose LCs, and graphene oxide LCs) is showcased. The review concludes with a perspective on the future scope, opportunities, and challenges in these truly advanced functional soft materials and their promising applications.

First-principles experimental demonstration of ferroelectricity in a thermotropic nematic liquid crystal: Polar domains and striking electro-optics.

Abstract: We report the experimental determination of the structure and response to applied electric field of the lower-temperature nematic phase of the previously reported calamitic compound 4-[(4-nitrophenoxy)carbonyl]phenyl2,4-dimethoxybenzoate (RM734). We exploit its electro-optics to visualize the appearance, in the absence of applied field, of a permanent electric polarization density, manifested as a spontaneously broken symmetry in distinct domains of opposite polar orientation. Polarization reversal is mediated by field-induced domain wall movement, making this phase ferroelectric, a 3D uniaxial nematic having a spontaneous, reorientable polarization locally parallel to the director. This polarization density saturates at a low temperature value of ∼6 µC/cm2, the largest ever measured for a fluid or glassy material. This polarization is comparable to that of solid state ferroelectrics and is close to the average value obtained by assuming perfect, polar alignment of molecular dipoles in the nematic. We find a host of spectacular optical and hydrodynamic effects driven by ultralow applied field (E ∼ 1 V/cm), produced by the coupling of the large polarization to nematic birefringence and flow. Electrostatic self-interaction of the polarization charge renders the transition from the nematic phase mean field-like and weakly first order and controls the director field structure of the ferroelectric phase. Atomistic molecular dynamics simulation reveals short-range polar molecular interactions that favor ferroelectric ordering, including a tendency for head-to-tail association into polar, chain-like assemblies having polar lateral correlations. These results indicate a significant potential for transformative, new nematic physics, chemistry, and applications based on the enhanced understanding, development, and exploitation of molecular electrostatic interaction.

Additive-Free MXene Liquid Crystals and Fibers

Abstract: The discovery of liquid crystalline (LC) phases in dispersions of two-dimensional (2D) materials has enabled the development of macroscopically aligned three-dimensional (3D) macrostructures. Here, we report the first experimental observation of self-assembled LC phases in aqueous Ti3C2T x MXene inks without using LC additives, binders, or stabilizing agents. We show that the transition concentration from the isotropic to nematic phase is influenced by the aspect ratio of MXene flakes. The formation of the nematic LC phase makes it possible to produce fibers from MXenes using a wet-spinning method. By changing the Ti3C2T x flake size in the ink formulation, coagulation bath, and spinning parameters, we control the morphology of the MXene fibers. The wet-spun Ti3C2T x fibers show a high electrical conductivity of ∼7750 S cm-1, surpassing existing nanomaterial-based fibers. A high volumetric capacitance of ∼1265 F cm-3 makes Ti3C2T x fibers promising for fiber-shaped supercapacitor devices. We also show that Ti3C2T x fibers can be used as heaters. Notably, the nematic LC phase can be achieved in other MXenes (Mo2Ti2C3T x and Ti2CT x ) and in various organic solvents, suggesting the widespread LC behavior of MXene inks.

High-efficiency improvement of thermal conductivities for epoxy composites from synthesized liquid crystal epoxy followed by doping BN fillers

Abstract: Liquid crystal epoxy resin presents high intrinsic thermal conductivity coefficient (λ). However, the complex molecular structure design and tedious synthesis process severely limit its rapid development and further industrial application. In this work, a kind of liquid crystal epoxy (LCE) based on biphenyl mesomorphic unit is synthesized from 4,4′-biphenol, triethylene glycol, and epichlorohydrin. Curing agent of 4,4′-diaminodiphenyl methane (DDM) and boron nitride (BN) fillers are both performed to prepare the intrinsic highly thermally conductive liquid crystal epoxy resin (LCER) and BN/LCER thermally conductive composites via casting method. LCE has been successfully synthesized with expected structure, presenting nematic liquid crystal with range of 135–165 °C. LCER shows liquid crystal property with intrinsic λ up to 0.51 W/mK, about 3 times higher than that of general bisphenol A epoxy resin (E−51, 0.19 W/mK). Simultaneously, LCER has good thermal stability with heat resistance index (THRI) being 183.9 °C. In addition, the λ values of the BN/LCER thermally conductive composites increase with the increasing loading of BN fillers. When the content of BN fillers is 30 wt%, the λ value of BN/LCER thermally conductive composites is 1.02 W/mK, twice as much as that of pure LCER, also much higher than that of 30 wt% BN/E−51 composites (0.52 W/mK).

Nematic superconductivity in twisted bilayer graphene

Abstract: Twisted bilayer graphene displays insulating and superconducting phases caused by flattening of its energy band. In the superconducting dome near hole half-filling, the threefold lattice rotation symmetry is broken, and the superconductor is also a nematic. The authors argue that superconductivity can be properly described by a patch model near twelve Van Hove points and show that there is nearly equal attractive interaction in two different superconducting channels. They go on to explicitly demonstrate that when both orders develop, the superconducting state is also a nematic.

Ferroelectric-Ferroelastic Phase Transition in a Nematic Liquid Crystal.

Abstract: Ferroelectric ordering in liquids is a fundamental question of physics. Here, we show that ferroelectric ordering of the molecules causes the formation of recently reported splay nematic liquid-crystalline phase. As shown by dielectric spectroscopy, the transition between the uniaxial and the splay nematic phase has the characteristics of a ferroelectric phase transition, which drives an orientational ferroelastic transition via flexoelectric coupling. The polarity of the splay phase was proven by second harmonic generation imaging, which additionally allowed for determination of the splay modulation period to be of the order of 5-10 microns, also confirmed by polarized optical microscopy. The observations can be quantitatively described by a Landau-de Gennes type of macroscopic theory.

Nematicity with a twist: Rotational symmetry breaking in a moiré superlattice

Abstract: Motivated by recent reports of nematic order in twisted bilayer graphene (TBG), we investigate the impact of the triangular moire superlattice degrees of freedom on nematicity. In TBG, the nematic order parameter is not Ising like, as in tetragonal crystals, but has a three-state Potts character related to the threefold rotational symmetry (C3z) of the moire superlattice. We find that, even in the presence of static strain that explicitly breaks the C3z symmetry, the system can still undergo a nematic-flop phase transition that spontaneously breaks in-plane twofold rotations. Moreover, elastic fluctuations, manifested as acoustic phonons, mediate a nemato-orbital coupling that ties the nematic director orientation to certain soft directions in momentum space, rendering the Potts-nematic transition mean field and first order. In contrast to the case of rigid crystals, the Fermi surface hot spots associated with these soft directions are maximally coupled to low-energy nematic fluctuations in the moire superlattice case.

Cellulose Nanocrystal Elastomers with Reversible Visible Color.

Abstract: Responsive photonic crystals have potential applications in mechanical sensors and soft displays; however, new materials are constantly desired to provide new innovations and improve on existing technologies. To address this, we report stretchable chiral nematic cellulose nanocrystal (CNC) elastomer composites that exhibit reversible visible color upon the application of mechanical stress. When stretched (or compressed) the colorless materials maintain their chiral nematic structure but the helical pitch is reduced into the visible region, resulting in coloration of the CNC-elastomer composite. By increasing the percentage elongation of the material (ca. 50-300 %), the structural color can be tuned from red to blue. The color of the materials was characterized by reflectance optical microscopy and reflectance circular dichroism to confirm the wavelength and polarization of the reflected light. We also probed the mechanism of the structural color using 2D-X-ray diffraction. Finally, by either water-patterning the starting CNC film, or by forming a CNC film with gradient color, through masked evaporation, we were able to prepare encoded stretchable chiral nematic CNC-elastomers.

Electric-Field-Regulated Energy Transfer in Chiral Liquid Crystals for Enhancing Upconverted Circularly Polarized Luminescence through Steering the Photonic Bandgap.

Abstract: Circularly polarized luminescent materials with high dissymmetry factor (glum ) have been attracting increasing attention due to their distinctive photonic properties. In this work, by incorporating upconversion nanoparticles (UCNPs) and CsPbBr3 perovskite nanocrystals (PKNCs) into a chiral nematic liquid crystal (N*LC), enhanced upconverted circularly polarized luminescence (UC-CPL) based on a radiative energy transfer (RET) process from UCNPs to CsPbBr3 PKNCs is successfully implemented. By locating the emission peak of CsPbBr3 PKNCs at the center of the photonic bandgap of N*LC, the maximum glum value of UC-CPL can be amplified to an extremely large value of 1.1. Meanwhile, upconverted emission of UCNPs can be significantly enhanced due to the band edge enhancement effect of the N*LC, subsequently enhancing the emission of the CsPbBr3 PKNCs through the RET process. In addition, an applied electric field can switch the upconverted emission of the UCNPs, as well as the RET process, enabling an electric-field-controlled UC-CPL switch.

Sequentially amplified circularly polarized ultraviolet luminescence for enantioselective photopolymerization.

Abstract: Chiral optical materials based on circularly polarized luminescence (CPL) have emerged rapidly due to their feasible applications in diverse fields of research. However, limited to the small luminescence dissymmetry factor (glum), real application examples have rarely been reported. Here, we present a complex system, which show intense circularly polarized ultraviolet luminescence (CPUVL) with large glum value, enabling a chiral UV light triggered enantioselective polymerization. By integrating sensitized triplet-triplet annihilation upconversion and CPL, both visible-to-UV upconversion emission and upconverted circularly polarized ultraviolet luminescence (UC-CPUVL) were obtained in the systems, built of chiral annihilator R(S)-4,12-biphenyl[2,2]paracyclophane (R-/S-TP), and a thermally activated delayed fluorescence (TADF) sensitizer. After dispersing this upconversion system into room-temperature nematic liquid crystal, induced chiral nematic liquid crystal could significantly amplify the glum value (0.19) of UC-CPUVL. Further, the UC-CPUVL emission has been used to trigger the enantioselective photopolymerization of diacetylene. This work paves the way for the further development of functional application of CPL active materials. Chiral functional materials with circularly polarized luminescence can be used in various applications but rarely reported. Here the authors show, a complex system, which show intense circularly polarized ultraviolet luminescence with large glum value, enabling a chiral UV light triggered enantioselective polymerization.

Flat-Panel Laser Displays Based on Liquid Crystal Microlaser Arrays

Abstract: Laser displays, benefiting from the characteristic merits of lasers, have led to the revolution of next-generation display technologies owing to their superior color expression. However, the acquis...

Reconfiguration of three-dimensional liquid-crystalline photonic crystals by electrostriction

Abstract: Natural self-assembled three-dimensional photonic crystals such as blue-phase liquid crystals typically assume cubic lattice structures. Nonetheless, blue-phase liquid crystals with distinct crystal symmetries and thus band structures will be advantageous for optical applications. Here we use repetitive electrical pulses to reconfigure blue-phase liquid crystals into stable orthorhombic and tetragonal lattices. This approach, termed repetitively applied field, allows the system to relax between each pulse, gradually transforming the initial cubic lattice into various intermediate metastable states until a stable non-cubic crystal is achieved. We show that this technique is suitable for engineering non-cubic lattices with tailored photonic bandgaps, associated dispersion and band structure across the entire visible spectrum in blue-phase liquid crystals with distinct composition and initial crystal orientation. These field-free blue-phase liquid crystals exhibit large electro-optic responses and can be polymer-stabilized to have a wide operating temperature range and submillisecond response speed, which are promising properties for information display, electro-optics, nonlinear optics, microlasers and biosensing applications.

From Equilibrium Liquid Crystal Formation and Kinetic Arrest to Photonic Bandgap Films Using Suspensions of Cellulose Nanocrystals

Abstract: The lyotropic cholesteric liquid crystal phase developed by suspensions of cellulose nanocrystals (CNCs) has come increasingly into focus from numerous directions over the last few years. In part, this is because CNC suspensions are sustainably produced aqueous suspensions of a fully bio-derived nanomaterial with attractive properties. Equally important is the interesting and useful behavior exhibited by solid CNC films, created by drying a cholesteric-forming suspension. However, the pathway along which these films are realized, starting from a CNC suspension that may have low enough concentration to be fully isotropic, is more complex than often appreciated, leading to reproducibility problems and confusion. Addressing a broad audience of physicists, chemists, materials scientists and engineers, this Review focuses primarily on the physics and physical chemistry of CNC suspensions and the process of drying them. The ambition is to explain rather than to repeat, hence we spend more time than usual on the meanings and relevance of the key colloid and liquid crystal science concepts that must be mastered in order to understand the behavior of CNC suspensions, and we present some interesting analyses, arguments and data for the first time. We go through the development of cholesteric nuclei (tactoids) from the isotropic phase and their potential impact on the final dry films; the spontaneous CNC fractionation that takes place in the phase coexistence window; the kinetic arrest that sets in when the CNC mass fraction reaches ∼10 wt.%, preserving the cholesteric helical order until the film has dried; the ’coffee-ring effect’ active prior to kinetic arrest, often ruining the uniformity in the produced films; and the compression of the helix during the final water evaporation, giving rise to visible structural color in the films.

Melting of a skyrmion lattice to a skyrmion liquid via a hexatic phase.

Abstract: The phase transition most commonly observed is probably melting, a transition from ordered crystalline solids to disordered isotropic liquids. In three dimensions, melting is a single, first-order phase transition. In two-dimensional systems, however, theory predicts a general scenario of two continuous phase transitions separated by an intermediate, oriented liquid state, the so-called hexatic phase with short-range translational and quasi-long-range orientational orders. Such hexatic phases occur in colloidal systems, Wigner solids and liquid crystals, all composed of real-matter particles. In contrast, skyrmions are countable soliton configurations with non-trivial topology and these quasi-particles can form two-dimensional lattices. Here we show, by direct imaging with cryo-Lorentz transmission electron microscopy, that magnetic field variations can tune the phase of the skyrmion ensembles in Cu2OSeO3 from a two-dimensional solid through the long-speculated skyrmion hexatic phase to a liquid. The local spin order persists throughout the process. Remarkably, our quantitative analysis demonstrates that the aforementioned topological-defect-induced crystal melting scenario well describes the observed phase transitions. While in 3D materials melting is a single, first-order phase transition, in 2D systems, it can also proceed via an intermediate phase. For a skyrmion lattice in Cu2OSeO3, magnetic field variations can tune this quasiparticle 2D solid into a skyrmion liquid via an intermediate hexatic phase with short-range translational and quasi-long-range orientational order.

Topological structure and dynamics of three-dimensional active nematics

Abstract: Topological structures are effective descriptors of the nonequilibrium dynamics of diverse many-body systems. For example, motile, point-like topological defects capture the salient features of two-dimensional active liquid crystals composed of energy-consuming anisotropic units. We dispersed force-generating microtubule bundles in a passive colloidal liquid crystal to form a three-dimensional active nematic. Light-sheet microscopy revealed the temporal evolution of the millimeter-scale structure of these active nematics with single-bundle resolution. The primary topological excitations are extended, charge-neutral disclination loops that undergo complex dynamics and recombination events. Our work suggests a framework for analyzing the nonequilibrium dynamics of bulk anisotropic systems as diverse as driven complex fluids, active metamaterials, biological tissues, and collections of robots or organisms.

Functional Ionic Liquid Crystals.

Abstract: Ionic liquid crystals have emerged as a new class of functional soft materials in the last two decades, and they exhibit synergistic characteristics of ionic liquids and liquid crystals such as mac...

Light- and Humidity-Responsive Chiral Nematic Photonic Crystal Films Based on Cellulose Nanocrystals.

Abstract: Light- and humidity-responsive chiral nematic photonic crystal (PC) films containing cellulose nanocrystals (CNCs) were fabricated. A photoactive polymer with hydrophilic groups, poly-(3,3'-benzophenone-4,4'-dicarboxylic acid dicarboxylate polyethylene glycol) ester, was coassembled with CNCs to form flexible iridescent films with a tunable chiral nematic order. In the coassembly process, the intermolecular hydrogen bonds of CNCs were weakened, which facilitated the fine regulation of the chiral PC nanostructure. The PC films displayed sensitive responses to both light and humidity. With increasing humidity from 30 to 100%, the chiral nematic helix pitch increased from 328 to 422 nm. The color of the PC films changed from blue to green, yellow, orange, and dark red with increasing relative humidity. Over 15 min of light irradiation, the absorption intensity of the films increased gradually. The light and humidity responses of the films were reversible. The films maintained their variable cholesteric liquid crystal texture and helical lamellar structure after light irradiation at different humidities. These PC films are expected to be useful in intelligent coatings and 3D printing.

Quenched nematic criticality and two superconducting domes in an iron-based superconductor

Abstract: The nematic electronic state and its associated critical fluctuations have emerged as a potential candidate for the superconducting pairing in various unconventional superconductors. However, in most materials their coexistence with magnetically ordered phases poses a significant challenge in determining their importance. Here, by combining chemical and hydrostatic physical pressure in FeSe0.89S0.11, we access a nematic quantum phase transition isolated from any other competing magnetic phases. From quantum oscillations in high magnetic fields, we trace the evolution of the Fermi surface and electronic correlations as a function of applied pressure and detect a Lifshitz transition that separates two distinct superconducting regions. One emerges from the nematic phase with a small Fermi surface and strong electronic correlations, while the other one has a large Fermi surface and weak correlations that promotes nesting and stabilization of a magnetically ordered phase at high pressures. The absence of mass divergence at the nematic quantum phase transition suggests that the nematic fluctuations could be quenched by the strong coupling to the lattice or local strain effects. A direct consequence is the weakening of superconductivity at the nematic quantum phase transition in the absence of magnetically driven fluctuations.

Optical properties of metasurfaces infiltrated with liquid crystals

Abstract: Optical metasurfaces allow the ability to precisely manipulate the wavefront of light, creating many interesting and exotic optical phenomena. However, they generally lack dynamic control over their optical properties and are limited to passive optical elements. In this work, we report the nontrivial infiltration of nanostructured metalenses with three respective nematic liquid crystals of different refractive index and birefringence. The optical properties of the metalens are evaluated after liquid-crystal infiltration to quantify its effect on the intended optical design. We observe a significant modification of the metalens focus after infiltration for each liquid crystal. These optical changes result from modification of local refractive index surrounding the metalens structure after infiltration. We report qualitative agreement of the optical experiments with finite-difference time-domain solver (FDTD) simulation results. By harnessing the tunability inherent in the orientation dependent refractive index of the infiltrated liquid crystal, the metalens system considered here has the potential to enable dynamic reconfigurability in metasurfaces.

Ferroelectric nematic liquid crystal, a century in waiting

Abstract: In PNAS, the liquid crystal group of the Soft Materials Research Center at the University of Colorado Boulder, led by N. A. Clark, reports on the discovery of a ferroelectric nematic fluid NF, an additional state of matter (Chen et al., ref. 1) (Fig. 1 A ). Such a phase has been expected at least since 1916 (2), but first-principle experiments have never demonstrated its existence until now. To many, the word “nematic” is associated with the informational revolution of the 20th century and portable displays enabled by this liquid crystal. That nematic (N), shown in Fig. 1 B and C , is a nonpolar version of the discovered nematic. Fig. 1. ( A and B ) Random selection of molecular dipoles in ferroelectric NF ( A ) and dielectric N ( B ) nematics. ( C ) Topological defects, disclinations, and a point defect–hedgehog, in N. ( D–F ) Domain walls in ferromagnets ( D ) and in NF ( E and F ). ( G and H ) Disclinations in N serve as seeds of domain walls in NF with different orientations of the polarization vector, weakly ( G ) and strongly ( H ) charged. Molecules of N, usually of a rod-like shape, align parallel to each other but otherwise are free to move around, showing no long-range positional order. The rods are 2 to 3 nm long, typically with chemically distinct ends, but molecular interactions do not distinguish between these ends and the fluid is nonpolar (Fig. 1 B ). The apolar character of N is captured by the identity property n ^ ≡ − n ^ of the headless vector n ^ , called the director, which specifies the average orientation of the molecules. The nonpolarity is also reflected in the name. The term nematic derives from the Greek νeμα, which reads “nema” and means “thread.” The word was invented by Friedel in 1922 (3), who … [↵][1]1Email: olavrent{at}kent.edu. [1]: #xref-corresp-1-1

Dual Stimuli-Responsive High-Efficiency Circularly Polarized Luminescence from Light-Emitting Chiral Nematic Liquid Crystals.

Abstract: Considerable luminescence dissymmetry factor (glum) is vital for application implementation of circularly polarized luminescence (CPL) materials. Moreover, a dual CPL switch has promising prospects...

New wide-stability four-ring azo/ester/Schiff base liquid crystals: synthesis, mesomorphic, photophysical, and DFT approaches

Abstract: New four-groups-based azo/ester/Schiff base liquid crystals, ((4-substitutedphenylimino)methyl)phenyl 4-[2-(4-alkoxyhenyl)diazenyl]benzoate, Ina–d, were synthesized and analyzed for their mesomorphic stability and optical activity. In these compounds, a terminal alkoxy group of variable chain length from n = 6 to n = 16 carbons is attached to the end of a phenylazo benzoate moiety and the other end of the molecules is connected to a different polar compact substituent X (CH3O, CH3, H, and Cl). FT-IR, 1H NMR, mass spectroscopy and elemental analysis were carried out for molecular structure confirmation of the prepared compounds. The mesomorphic properties were confirmed using a combination of differential scanning calorimetry (DSC) and polarized light microscopy (PLM). The photophysical property was studied by UV-vis spectroscopy. All the prepared homologous series exhibited high thermal stability with a wide-temperature mesomorphic range. The thermal and geometrical parameters of the investigated compounds were estimated by density functional theory (DFT). The results revealed that all the compounds were not completely planar with a relatively high twisting moiety at the CHN part and their twist angles were affected by the electronic nature of the attached X group. Moreover, the calculated quantum chemical parameters as determined by the DFT approach of the investigated compounds were related to the experimentally determined values of the mesophase thermal stability (Tc) and mesophase temperature ranges (ΔTSmA and ΔTN) as well as the type of the mesophase.

Chiral Platinum-Based Metallomesogens with Highly Efficient Circularly Polarized Electroluminescence in Solution-Processed Organic Light-Emitting Diodes

Abstract: Circularly polarized luminescence (CPL) is of interest due to its wide potential application in semiconductors. To balance the emission efficiency and luminescence dissymmetry factor (gPL) of a CPL emitter, in this context, two chiral, phosphorescent and liquid-crystalline cyclometalated platinum complexes, abbreviated R-Pt and S-Pt, are prepared. The complexes, which show an intense green emission at 504 nm both in solution and in the solid state, contain a simple, ortho-metalated 2-phenylpyridine unit functionalized with a chiral 2-octanol chain, with liquid crystallinity being induced by modifying the β-diketonato ligand with mesogenic groups. Interestingly, both the chiral smectic (SmA*) and nematic (N*) phases are found by a combination of polarized optical microscopy, differential scanning calorimetry, and small-angle X-ray scattering. By annealing, distinct CPL emission is achieved in the solid state with a gPL around 0.02. Employing the chiral platinum complexes as the dopant, solution-processable organic light-emitting diodes present an external quantum efficiency of 11.3% and strong, circularly polarized electroluminescence with an extremely high luminescence dissymmetry value (gEL) of 0.06 after annealing at 100 °C. This work opens an avenue for designing CPL-active emitters with high emission efficiency and high dissymmetry factor.

Three-state nematicity in the triangular lattice antiferromagnet Fe1/3NbS2.

Abstract: Nematic order is the breaking of rotational symmetry in the presence of translational invariance. While originally defined in the context of liquid crystals, the concept of nematic order has arisen in crystalline matter with discrete rotational symmetry, most prominently in the tetragonal Fe-based superconductors where the parent state is four-fold symmetric. In this case the nematic director takes on only two directions, and the order parameter in such 'Ising-nematic' systems is a simple scalar. Here, using a spatially resolved optical polarimetry technique, we show that a qualitatively distinct nematic state arises in the triangular lattice antiferromagnet Fe1/3NbS2. The crucial difference is that the nematic order on the triangular lattice is a [Formula: see text] or three-state Potts-nematic order parameter. As a consequence, the anisotropy axes of response functions such as the resistivity tensor can be continuously reoriented by external perturbations. This discovery lays the groundwork for devices that exploit analogies with nematic liquid crystals.

Tunable Metasurface Inverse Design for 80% Switching Efficiencies and 144° Angular Deflection

Abstract: Tunable metasurfaces have demonstrated the potential for dramatically enhanced functionality for applications including sensing, ranging and imaging. Liquid crystals (LCs) have fast switching speed...

Visible-Light-Driven Halogen Bond Donor Based Molecular Switches: From Reversible Unwinding to Handedness Inversion in Self-Organized Soft Helical Superstructures

Abstract: Visible-light-driven molecular switches endowing reversible modulation of the functionalities of self-organized soft materials are currently highly sought after for fundamental scientific studies and technological applications. Reported herein are the design and synthesis of two novel halogen bond donor based chiral molecular switches that exhibit reversible photoisomerization upon exposure to visible light of different wavelengths. These chiral molecular switches induce photoresponsive helical superstructures, that is, cholesteric liquid crystals, when doped into the commercially available room-temperature achiral liquid crystal host 5CB, which also acts as a halogen-bond acceptor. The induced helical superstructure containing the molecular switch with terminal iodo atoms exhibits visible-light-driven reversible unwinding, that is, a cholesteric-nematic phase transition. Interestingly, the molecular switch with terminal bromo atoms confers reversible handedness inversion to the helical superstructure upon irradiation with visible light of different wavelengths. This visible-light-driven, reversible handedness inversion, enabled by a halogen bond donor molecular switch, is unprecedented.

Shaping colloidal bananas to reveal biaxial, splay-bend nematic, and smectic phases

Abstract: Understanding the impact of curvature on the self-assembly of elongated microscopic building blocks, such as molecules and proteins, is key to engineering functional materials with predesigned structure We develop model “banana-shaped” colloidal particles with tunable dimensions and curvature, whose structure and dynamics are accessible at the particle level By heating initially straight rods made of SU-8 photoresist, we induce a controllable shape deformation that causes the rods to buckle into banana-shaped particles We elucidate the phase behavior of differently curved colloidal bananas using confocal microscopy Although highly curved bananas only form isotropic phases, less curved bananas exhibit very rich phase behavior, including biaxial nematic phases, polar and antipolar smectic-like phases, and even the long-predicted, elusive splay-bend nematic phase