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As the temperature decreases, rigid anisotropic molecules that usually incorporate polar groups, aromatic rings or multiple bonds, orient along a common direction, eventually forming liquid-crystalline phases under specific thermodynamic conditions. This study explores the phase behavior and dynamics of board-shaped mesogens with a 1,4,5,8-tetraphenyl-anthraquinone core and four lateral arms forming an oligo(phenyleneethynylene) scaffold. These molecules are promising candidates for forming the elusive biaxial nematic phase. Through atomistic molecular dynamics simulations, we observe the formation of nematic and smectic liquid crystals, in qualitative agreement with experimental observations. To characterize the structure, we compute pair correlation functions along relevant symmetry directions and the nematic order parameter, which indicate a dominant uniaxial ordering with very weak biaxiality. In addition, we analyze the dynamics of our board-shaped mesogens along and perpendicular to the nematic director, revealing an intriguing non-Gaussian behavior and dynamical heterogeneities, with coexisting slow and fast molecules. Building on our recent simulations at the colloidal scale, which demonstrated that monodisperse board-like particles are unable to form biaxial nematics while polydisperse particles can, we hypothesize that a similar behavior may occur at the molecular scale in mixtures of molecules. Although pure-component molecular systems reveal weak biaxiality, our findings suggest that investigating mixtures of the most promising candidates, those molecules that form nematic or smectic phases, could uncover conditions conducive to the formation of biaxial nematic liquid crystals. [ABSTRACT FROM AUTHOR]

A coarser model for the Gay-Berne mesogen is developed using the interaction potential from the Approximate Non-Conformal (ANC) theory. The ANC potential contains both repulsive and attractive contributions. We modify intermolecular attractions by conditioning them with a Hess-Su orientation-dependent term. This imparts an anisotropic contribution to the energy of the system. The softness parameter s of the ANC potential is probed to qualitatively identify a threshold capable of sustaining a nematic phase. We construct phase diagrams for each value of s from molecular dynamics simulations and characterise bulk samples to outline phase regions. We find that a softness parameter $ s \sim 0.6 $ s ∼ 0.6 or higher supports the emergence of a nematic phase. The stability of the nematic region is enhanced as $ s\to 1 $ s → 1 , corresponding to the conventional Lennard-Jones interaction. The stability of the nematic phase for nearly-spherical mesogens with increasing s leads to a gradual loss in spherical symmetry despite no imposed shape anisotropy. Thus, the energy anisotropy becomes more pronounced and is capable of prompting the emergence of the nematic phase in this model. [ABSTRACT FROM AUTHOR]

Liquid crystal-forming cyanobiphenyls are truly extraordinary molecules that have had an enormous impact on liquid crystal research and applications since they were first synthesised. This impact is, on the one hand, due to the exceptionally convenient physical properties of the main characters, 5CB and 8CB, allowing easy experiments at room temperature, as well as their commercial availability at reasonable cost. On the other hand, the cyanobiphenyl chemical structure leads to some quite peculiar characteristics in terms of organisation at the molecular scale, which are sometimes well recognised and even utilised, but often the awareness of these peculiarities is not strong. This perspective article reviews the use of cyanobiphenyls in making liquid crystal shells and liquid crystal core fibres, in sensing, as a medium for simultaneously aligning and dispersing carbon nanotubes, and as highly useful solvents for reactive mesogens that can be polymerised into anisotropic networks. This choice is very much motivated by how cyanobiphenyls have impacted our group's research throughout the years, which is the basis for the examples I provide. Nevertheless, I believe they serve well to illustrate the immense usefulness of cyanobiphenyls in innovating research and applications related to liquid crystals. [ABSTRACT FROM AUTHOR]

The recent identification of ferroelectricity within the nematic phase of liquid crystals has triggered significant interest. However, prior to this discovery; the potential existence of ferroelectricity in the nematic phase had already been investigated in the context of cybotactic nematic phases of liquid crystals. Ferroelectricity has previously been reported in chiral and achiral smectic phases. While the presence of nano-sized smectic clusters in the nematic phase of rod-shaped molecules, termed as cybotactic nematic, was recognised, it did not earn substantial attention. However, the cybotactic nematic phase in bent-core mesogens has gained significant attention due to its unconventional ferroelectric-like behaviour. To link the recent advancements in understanding ferroelectricity in the nematic phase, a comprehensive review has been conducted on the cybotactic nematic phase. This review encompasses a foundational explanation of the cybotactic model, followed by an overview of cybotactic phases in rod-shaped mesogens. The central focus lies in evaluating cybotactic phases within bent-core nematic systems, covering early debates, fundamental experimental evidences, and a compilation of mesogens that exhibit the cybotactic nematic phase. Furthermore, the review describes into the physical attributes of mesogens featuring cybotactic nematic phases, including discussions on repolarisation, dielectric properties, and optical characteristics. [ABSTRACT FROM AUTHOR]

In this work, we aim to model the reorientation process of mesogens in nematic liquid crystal elastomers within the context of dynamics. We consider a continuum model with separate mappings for the deformation of the monolithic material and the orientation of the nematic director, where the latter describes the inclination of the mesogens. We achieve the inextensibility of the nematic director through the introduction of drilling degrees of freedom. We combine this approach with the application of the principle of virtual power and a mixed finite element formulation, in order to formulate distinct momentum and angular momentum balance laws for the two separate mappings. Furthermore, we include in our continuum model a volume load and a surface load associated only with the orientation mapping. We show in the presented three numerical examples that our formulation enables the fulfillment of all momentum and angular momentum balance laws. [ABSTRACT FROM AUTHOR]

Liquid crystals (LCs), whose refractive index can be changed by light irradiation, can be used as photoresponsive optical materials. In this study, an LC viologen was proposed as a novel photoresponsive compound that induced a change in the alignment of LC molecules (mesogens). An extended viologen with an asymmetric core, that exhibits a low-order LC phase at room temperature, was mixed with the well-known nematic LC compound (5CB) to prepare homogeneously aligned films. The change in the alignment of the mesogens was successfully induced by triggering a one-electron reduction reaction of the viologen moieties by light irradiation. [ABSTRACT FROM AUTHOR]

Magnetorheological fluids (MRFs) are promising smart materials that can respond to an external field. In order to obtain stable suspension and investigate the settlement law of these synthesised MRFs, polymerised ionic liquid crystalline (PILC) ferroferric oxide nanocomposites (Fe3O4@PILCs), the dispersed phase in MRFs, were obtained by self-assembly of magnetic Fe3O4 nanoparticles with PILCs. The structural properties, thermotropic liquid crystal characteristics, morphology and microscopic magnetic response characteristics were investigated in this study. Fe3O4@PILCs showed nematic liquid crystal behaviour, and the mesogenic phase range was affected by the content of cholesteryl-based LC mesogen containing carboxylic acid groups. Series of MRFs were prepared by the Fe3O4@PILCs with 5% particles mass fractions in different volume fractions. The settlement stability as well as the settlement laws was investigated comprehensively and systematically for these MRFs. The Fe3O4@PILC-based MRFs exhibited better sedimentation stability than the bare Fe3O4-based MRFs, indicating that the Fe3O4 particles self-assembled with PILCs could reduce the density of the dispersed phase and showed the good compatibility with silicone oil carrier fluid. The sedimentation velocity curves of the Fe3O4@PILC-based with different particle volume fractions were investigated by use of some relevant theoretical models, indicating that they were the most consistent with the Dick's model. [ABSTRACT FROM AUTHOR]

The synthesis of bent-shaped mesogens and mesogenic dimers has renewed the field of liquid crystals in many ways during the previous decades, for example, through the discovery of 'exotic' mesophases such as the twist-bend nematic phase and the biaxial SmA phase (SmAb). Recently, we reported on the observation of a SmAb with a bent-shaped dimer, and on its fast electro-optic effect that we interpreted as a biaxial Fréedericksz transition (BFrTr) of the secondary m-director under applied electric field (C. Meyer et al., Phys. Rev. X, 11, 031012 (2021)). In this study, we used dielectric and birefringence techniques to directly measure the splay, K 11 m , and bend, K 33 m , elastic constants that characterise the elastic distortion modes of the m-director. We observed that during the BFrTr, domains of opposite tilt appear and are often enclosed in elliptical defect loops, just like those observed during the usual Fréedericksz transition of common nematics, which allowed us to obtain the third (twist) elastic constant K 22 m , from the defect loop ellipticity. Although K 11 m and K 33 m are of the same order of magnitude as K 11 and K 33 in the nematic phase of bent-shaped dimers, K 22 m is an order of magnitude smaller than K 11 m and K 33 m and also than K 22 of 5CB. We argue that these features could be generic for the intercalated SmAb phase of bent-shaped dimers. [ABSTRACT FROM AUTHOR]

Since their discovery in 1888, liquid crystals (LCs) have attracted an unceasing research interest due to their exceptional electro-optical properties that are crucial in the development of displays and modern photonic systems. The vast majority of research works in this domain include the usage of nematic liquid crystals (NLCs) which are repellent for the high-speed optical photonic devices due to their slow electro-optical response. However, in context of electro-optical response time and switch-on voltage, the NLCs still have a huge space to be improved in comparison to other competitive technological solutions. Alternatively, the most promising candidates for development of the next-generation LC-based photonic devices are chiral smectic C (SmC*) LCs, also known as ferroelectric liquid crystals (FLCs) with their microseconds response time and low power consumption. This review comprehensively evinces the recent advancement on the FLC-based photonic devices such as gratings, lenses, spatial light modulators, waveguides, etc. along with the various electro-optical switching modes in these devices. We have also discussed the boon and bane of the FLC materials which is essentially important for their futuristic photonic applications. [ABSTRACT FROM AUTHOR]

Two series of fluorene-core compounds were successfully synthesised, one series of compounds have different rigid conjugated structures, and the other series of compounds have different substituted dialkyl chains at the 9-position of fluorene core. The thermotropic mesomorphic behaviours and fluorescence characteristics of the synthesised compounds were investigated. It was found that these derivatives exhibited well fluorescence performance and wide mesophases range up to 196°C. The short dialkyl chains substituted at the fluorenyl 9-position can improve the solubility of the compounds while maintaining the mesogenic properties. It was also found that the fluorene-derived compounds as dopants of chiral nematic liquid crystal can effectively stabilise the double-twisted structure due to the biaxiality of fluorene core, so as to induce the emergence of blue phase or broaden its temperature range. [ABSTRACT FROM AUTHOR]

In 1976, Meyer predicted that bend distortions of the nematic director field are complemented by deformations of either twist or splay, yielding twist-bend and splay-bend nematic phases, respectively. Four decades later, the existence of the splay-bend nematic phase remains dubious, and the origin of these spontaneous distortions uncertain. Here, we conjecture that bend deformations of the nematic director can be complemented by simultaneous distortions of both twist and splay, yielding a twist-splay-bend nematic phase. Using theory and simulations, we show that the coupling between polar order and bend deformations drives the formation of modulated phases in systems of curved rods. We find that twist-bend phases transition to splay-bend phases via intermediate twist-splay-bend phases, and that splay distortions are always accompanied by periodic density modulations due to the coupling of the particle curvature with the non-uniform curvature of the splayed director field, implying that the twist-splay-bend and splay-bend phases of banana-shaped particles are actually smectic phases. The so-called twist-bend and splay-bend nematic liquid crystal phases are important concepts for studying bent-core mesogens. Chiappini et al. use a theory/simulation approach to suggest that the transition proceed via a twist-splay-bend phase which may be obscured by density modulations. [ABSTRACT FROM AUTHOR]

Fabricating functional materials via molecular self-assembly is a promising approach, and precisely controlling the molecular building blocks of nanostructures in the self-assembly process is an essential and challenging task. Blue phase liquid crystals are fascinating self-assembled three-dimensional nanomaterials because of their potential information displays and tuneable photonic applications. However, one of the main obstacles to their applications is their narrow temperature range of a few degrees centigrade, although many prior studies have broadened it to tens via molecular design. In this work, a series of tailored uniaxial rodlike mesogens disfavouring the formation of blue phases are introduced into a blue phase system comprising biaxial dimeric mesogens, a blue phase is observed continuously over a temperature range of 280 °C, and the range remains over 132.0 °C after excluding the frozen glassy state. The findings show that the molecular synergistic self-assembly behavior of biaxial and uniaxial mesogens may play a crucial role in achieving the ultrastable three-dimensional nanostructure of blue phases. Blue phases are spatially ordered yet fragile liquid crystalline structures, bearing applications in optoelectronics and photonics. Hu et al. show that self-assembly within a mixture of different mesogens may significantly broaden the temperature range over which they are stable. [ABSTRACT FROM AUTHOR]

Liquid crystal lenses have promise in optical systems owing to their tunability combined with low electrical power, cost, and weight. A good example of such a system is switchable contact lenses for the correction of age‐related presbyopia. Sufficiently large phase modulation can be done using nematic liquid crystals in a meniscus lens configuration. However, the birefringent materials are inherently polarisation dependent, usually requiring orthogonal polarisations to be focussed separately. A novel method is presented for producing polarisation independent lenses based on reactive mesogens. Results are presented for a 2‐level and 3‐level diffractive Fresnel lenses, and the promise of the technique for use in refractive lenses such as contact lenses is discussed. [ABSTRACT FROM AUTHOR]

Nematic liquid crystals (NLCs) absorbed in a nonwoven of surface-treated silica nanofibres (SiO2-NFs) orient the director along the nonwoven thickness direction if the NLCs prefer homeotropic anchoring onto the fibre surface. The nonwoven has vacant spaces with the dimensions of 0.3 and 0.6 μm in the thickness and cross directions, respectively, bordered with SiO2-NFs with 93 nm in diameter. The SiO2-NF surface was treated with a silane-coupling agent to induce the homeotropic anchoring of NLC mesogens onto the surface. The nematic director is arranged radially from the fibres although it is more severely constrained by the proximity between fibre surfaces along the thickness direction. Consequently, the NLCs can align along the nonwoven thickness direction involving −1/2 wedge disclinations on both sides of the fibres. [ABSTRACT FROM AUTHOR]

Liquid crystal lenses have promise in optical systems owing to their tunability combined with low electrical power, cost and weight. A good example of such a system is switchable contact lenses for the correction of age‐related presbyopia. Large phase modulation can be done using nematic liquid crystals. However, the birefringent materials are inherently polarisation dependent, usually requiring orthogonal polarisations to be focused separately. A novel method is presented for producing polarisation independent lenses based on reactive mesogens. [ABSTRACT FROM AUTHOR]

Abstract The possible existence of a ferroelectric nematic phase has been challenging liquid crystal scientists since it was first envisaged about 30 years ago. At present, an undisputable proof of proper ferroelectricity in low-molecular weight thermotropic nematics is still missing. However, over the last decade several groups have reported the observation of a ferroelectric-like switching behavior in the nematic phase of a number of bent-core mesogens. This effect is generally ascribed to polar clusters of molecules, known as cybotactic groups, permeating the nematic phase. In the unperturbed state the cluster dipoles are randomly oriented, so that the phase is macroscopically uniaxial and apolar; however, an external field exceeding a threshold is able to align the cluster dipoles, inducing the transition to a switchable polar and biaxial state. Even though this behavior clearly differs from that expected in a proper ferroelectric liquid crystal, it still deserves considerable interest for its potential implications from both a fundamental and a technological point of view. Here we review the studies devoted to this extraordinary effect, both experiments and simulations, and discuss the open questions that still remain unanswered. Highlights • Over the last decade a number of bent-core nematics have been observed to exhibit a ferroelectric-like switching response. • This effect is ascribed to the cybotactic order of the nematic phase, i.e. to the presence of nano-sized polar clusters. • An external electric field can align the cluster dipoles inducing a switchable, macroscopic polar and biaxial phase. • We review the evidences for this effect coming from multiple experimental investigations and molecular simulations. [ABSTRACT FROM AUTHOR]

Polymer network liquid crystals (PNLCs) whose optical transmittance state switches between transparence at low temperatures and haze at high temperatures were fabricated from mixtures of nematic liquid crystals (LCs) and reactive mesogens (RMs). This PNLC structure is simple but effective, namely, consists of micro-scale domains of orientation-ordered LCs and anisotropically polymerized RMs. The domains form through photopolymerization induced phase separation with inhomogeneous irradiation projected by laser speckling techniques. This irradiation method enables you to control the size and shape of phase-separation domains, and these PNLCs can be applied to novel thermoresponsive optical devices; optical isolators, thermometric sheets, and smart windows. [ABSTRACT FROM AUTHOR]

We present a robust method to prepare thin oriented nematic liquid crystalline elastomer-polymer (LCE-polymer) core-sheath fibers. An electrospinning setup is utilized to spin a single solution of photo-crosslinkable low molecular weight reactive mesogens and a support polymer to form the coaxial LCE-polymer fibers, where the support polymer forms the sheath via in situ phase separation as the solvent evaporates. We discuss the effect of phase separation and compare two different sheath polymers (polyvinylpyrrolidone and polylactic acid), investigating optical and morphological properties of obtained fibers, as well as the shape changes upon heating. The current fibers show only irreversible contraction, the relaxation most likely being hindered by the presence of the passive sheath polymer, increasing in stiffness on cooling. If the sheath polymer can be removed while keeping the LCE core intact, we expect LCE fibers produced in this way to have potential to be used as actuators, for instance in soft robotics and responsive textiles. [ABSTRACT FROM AUTHOR]

A liquid crystalline polymethacrylate having two cyclohexylphenyl mesogens on its side-chain (PMG0) was synthesized by the radical polymerization of the corresponding methacrylate monomer (MG0). PMG0 exhibited a smectic A phase around room temperature showing a focalconic fan texture in POM observations and a broad diffusion in a wide angle range of its WAXD profile. Upon slow cooling at −1 °C min−1from the isotropic melt, PMG0 exhibited spontaneous homeotropic alignment between two native glass surfaces. A mixture of the commercial nematic liquid crystal (ZLI-4792) containing 1.0 wt% PMG0 also exhibited a homeotropic alignment, which easily covered hydrophilic surfaces such as glass or polyacrylamide. [ABSTRACT FROM PUBLISHER]

Phase behaviors of two homologous binary systems of 4-alkyl-4′-cyanobiphenyl (nCB, n being the number of carbon atoms in the alkyl chain) and 4-alkoxy-4′-cyanobiphenyl (nOCB) were investigated. Their phase diagrams were drawn against an averaged chain length, n*. The phase boundary curves between neamtic (N) and smectic Ad (SmAd) phases in nCB/mCB (n = 3-6; m = 8, 9) binary systems were classified into four depending on four combinations of even- and odd-numbered n and m; even/even, odd/even, even/odd, and odd/odd. The similar odd-even effect was confirmed for nOCB/mOCB (n = 5, 6; m = 8, 9) binary systems. To elucidate the odd-even effect on the phase diagrams, the SmAd structures were investigated through an analysis of n (n*) dependence of the layer spacing of the SmAd structure, dSmAd, of neat nCB (n = 8-10), neat nOCB (n = 8-10), and nCB/8CB (n = 0-7) binary mixtures. The odd-even effect, the behavior of 0CB/8CB system, and the difference between nCB and nOCB were clarified based on their SmAd structures. [ABSTRACT FROM AUTHOR]

The discovery of the oblique chiral (or, the twist-bend, NTB) nematic phase predicted for bent-core mesogens has engendered much interest due to its unique structure and physical properties, and the possibility of use in the next generation of fast electro-optic technology. Bimesogenic calamitic as well as bent-core mesogens are found to form the NTBphase. Here, we report direct measurements of the temperature dependence of the conical tilt and the evidence of volcano-like orientational distribution of molecules in the NTBphase. Optical and x-ray scattering investigations of two single-component calamitic bimesogens and their mixtures show that, while the Maier–Saupe orientational distribution function (ODF) is valid for the higher temperature nematic phase, a generalised expansion in terms of even Legendre functions is needed for the NTBphase. Temperature dependence of the ODFs and the order parameters 〈P2(cosβ)〉, 〈P4(cosβ)〉, and 〈P6(cosβ)〉 has been measured in both phases. The parameters 〈P2(cosβ)〉 and 〈P4(cosβ)〉 increase/decrease in the N/NTBphase with decreasing temperature, while 〈P6(cosβ)〉 remains vanishingly small for all samples. The value of 〈P4(cosβ)〉 becomes negative in the NTBphase confirming a conical distribution of molecules as they follow a helical trajectory keeping the local director tilted at an angle αwrtthe macroscopic director. The heliconical tilt calculated from ODFs, exhibits a power law behaviour with temperature, vanishing at the transition to the N phase. [ABSTRACT FROM PUBLISHER]

The paper reviews assignment of the low-temperature nematic phase observed in simple bimesogenic or dimeric systems based on cyanobiphenyls and difluoroterphenyls to the twist-bend nematic phase, NTB, using a range of experimental techniques. These include DSC, X-rays, Polarising Microscopy, electro-optics, birefringence and measurements of the electroclinic effect arising from flexoelectricity. An emphasis is laid on the observations of the chiral domains of opposite handedness at zero field in an otherwise achiral liquid crystalline system in this phase. These observations are a direct consequence of the structure of the twist-bend phase predicted by Ivan Dozov for achiral bent core molecules. The paper reviews the electro-optic phenomena and the observed electroclinic effect and how these observations assign it as the NTBphase. Results of the nanoscale helical pitch measurements using freeze-fracture microscopy are reviewed and discussed briefly. Results of the measurements of elastic constants especially close to the N–NTBtransition are also reviewed. [ABSTRACT FROM PUBLISHER]

Two series of bimesogens with phenyl benzoate mesogenic units were prepared: one series having a heptamethylene spacer and the other a pentamethylene spacer with two ether-linking groups. These materials were prepared to provide experimental backing to the widely held hypothesis that methylene-linked bimesogens are more likely to exhibit the twist-bend nematic mesophase than their ether-linked counterparts. Several of the methylene-linked materials exhibited nematic and NTBmesophases, whereas the analogous ether-linked materials gave only nematic phases albeit with significantly higher clearing points. Virtual N–NTBtransition temperatures for both methylene- and ether-linked bimesogens were extrapolated by constructing binary phase diagrams with the well-studied twist-bend material CB9CB. Contrary to our expectations these virtual transition temperatures were in most cases higher for the ether-linked bimesogens than in the analogous methylene compounds, this runs counter to reported theories and hypotheses that the incorporation of ether-linking groups should serve to destabilise the NTBphase. [ABSTRACT FROM PUBLISHER]

Since its theoretical prediction in 1970, the search for the biaxial nematic phase in thermotropic systems has challenged generations of liquid crystal scientists. Over the last 10 years, bent-core mesogens have drawn much interest as promising candidates for nematic biaxiality. However, despite a number of disputed claims, conclusive evidence of proper (spontaneous and macroscopic) biaxial order in these materials is still missing. By contrast, it is now widely recognised that biaxiality exists on a local scale, in the form of nano-sized clusters of molecules (cybotactic groups) possessing smectic-like positional order and biaxial orientational order. This article provides a review of X-ray diffraction studies on biaxiality and cybotaxis in bent-core nematics, discussing the most relevant issues related to this research field. [ABSTRACT FROM PUBLISHER]

Hockey-stick-shaped molecules were newly synthesised to obtain pseudo-rodlike molecules. The designed molecules consist of a polar terminal ring (i.e. 2,3,4-, 2,4,6- or 3,4,5-trifluorophenyl group), a rigid middle block (i.e. four rings with aligned ester linkages) and a flexible terminal chain (i.e. dodecyloxy group). We found that the compounds with 2,3,4- and 3,4,5-trifluorophenyl groups formed a smectic A mesophase with head-to-head bi-layer building blocks, whereas the compound with 2,4,6-trifluorophenyl group formed a nematic mesophase. This might be concerned with the behaviour of pseudo-rodlike molecules [ABSTRACT FROM AUTHOR]

We present systematic experimental data on high resolution measurements of temperature dependence of optical birefringence (Δn) in a binary liquid crystalline system comprising calamitic 4-cyano-4′-octyloxybiphenyl (8OCB) and a hockey stick-shaped compound, 4-(3-decyloxyphenyliminomethyl) phenyl 4-decyloxycinnamate (SF7). The hockey stick-shaped mesogen shows a smectic A (SmA) phase in addition to two polymorphic tilted smectic phases. From an analysis of the Δn data, a quotient Q(T) has been derived which exhibits power law divergences both above and below the smectic A-nematic (SmA-N) phase transition. A noticeable shrinkage in width of the nematic range has been observed for a small increase in concentration of the angular mesogenic dopant. In the vicinity of the SmA-N phase transition, the values of effective critical exponent (α′), characterizing the critical fluctuation at this transition, have appeared to be in between those predicted by the 3D- XY and tricritical hypothesis. Furthermore, with increasing hockey stick-shaped molecular concentration, the SmA-N transition shows a tendency to be driven towards a first order nature. [ABSTRACT FROM AUTHOR]

The primary research goal within contemporary liquid crystalline display industry is to discover new materials exhibiting phase temperature range and properties useful for display application. In this work, we studied five binary mixtures composed of different concentrations of bent-core and calamitic compounds. Pure compounds and selected mixtures were studied by polarizing optical microscopy, differential scanning calorimetry, and X-ray diffractometry, as well as by semi-empirical quantum-chemical calculations. Phase transition types, temperatures, and enthalpies were determined. Molecular packaging in the nematic mesophase is proposed. All studied mixtures exhibit the nematic phase of wide temperature range near to the room temperature. [ABSTRACT FROM AUTHOR]

In this work, studies of the thermotropic and thermo-optical properties in five homogeneous mixtures of 4-n-alkyl-4′-cyanobiphenyl mesogens have been carried out. Temperature behavior of the mean refractive index n , ordinary n o and extraordinary n e refractive indices has been investigated. The principal polarizabilities α 0 and α e , effective geometry parameter α eg and average polarizability α ave were calculated using the internal field model (Vuks approach). Behavior of the birefringence Δ n and the anisotropy of polarizability Δ α as a function of temperature, and the order parameter in regions of the smectic A – nematic , nematic – isotropic liquid and smectic A – isotropic liquid phase transitions are discussed. [ABSTRACT FROM AUTHOR]

We have proposed a hybrid alignment nematic liquid crystal cell using a polymer-stabilized technology. The cell shows a reverse mode scattering property and is transparent at any viewing angle in the off-state. The cell turns to opaque in the on-state and has an asymmetrical scattering property at incident angles. Applying the cell to a smart glass, the cell can selectively scatter a midday sunlight with a function of window blinds. In a polymerization process, an ultraviolet (UV) penetration depth is carefully considered, which results in a change of polymer morphology. The UV irradiation from a homogeneous alignment substrate side causes a polymer-rich layer near the substrate and the stronger scattering in the on-state. [ABSTRACT FROM AUTHOR]

We have synthesized a new series of all-organic paramagnetic liquid crystalline (LC) compounds, which include a five-membered ring nitroxide radical (NR) moiety in the mesogen core and fluorine atoms as terminal substituents. These new compounds are the structural analogs of the previously reported NR-LC compounds, and showed remarkable fluorine substituent effects. The introducing fluorine atom into terminal unit stabilizes nematic phase. However, an excess of fluorination leads to the destabilization of nematic phase. [ABSTRACT FROM AUTHOR]

We report the transition temperatures for several series of structural variations on bent-core mesogens (BCMs) derived from the asymmetric oxazole biphenol mesogenic core. Trimethyl-substituted mesogens exhibit nematic phases that can be supercooled to room temperature. Preliminary X-ray diffraction (XRD) results confirm a cybotactic supramolecular organisation in these nematics; moreover, the splitting of the diffuse wide-angle XRD feature observed in trimethylated mesogens points to an enhanced biaxial orientational correlation in the transverse molecular packing compared to other BCMs. Finally, one of the trimethyl-substituted mesogens shows the formation of a room temperature metastable fibre-like crystalline order when supercooled in a magnetic field. [ABSTRACT FROM PUBLISHER]

In this work, we present the first part of a study into the relationship between molecular structure and the occurrence of the ‘twist-bend nematic phase’ (NTB). Given the large amount of chemical space that might reasonably be expected to give rise to the NTBphase, this paper is only concerned with methylene-linked bimesogens bearing polar terminal groups based on the initial work of George Gray on cyanobiphenyls. As with other studies, we find that the NTBphase is observed only for materials that contain an odd number of methylene units in the spacer chain. It also appears that, in a given series of materials, there is a weak negative correlation between the dipole moment of the individual mesogenic units and the thermal stability of the NTBphase. Furthermore, we find that increasing the length–breadth ratio of the individual mesogenic units also provides a significant increase in the thermal stability of the NTBphase. The electrooptic behaviour of two materials, one with a terminal nitrile unit and one with an isothiocyanate group, was investigated. The NTBphase of the NCS-terminated material can be switched with a large applied voltage (20 V μm−1); however, the analogous nitrile-terminated material showed no electrooptic response under these conditions. Either the threshold voltage to switching is simply lower for isothiocyanate materials than nitriles or that there is more than one phase currently identified as the twist-bend nematic. [ABSTRACT FROM PUBLISHER]

A liquid crystalline dendrimer having a cinnamate mesogen containing an azobenzene moiety (D-6AC2) was prepared as an alignment agent of nematic liquid crystals for a planar homogeneous alignment.D-6AC2is a thermotropic liquid crystal showing smectic phases. A mixture of ZLI-4792 with 1wt% ofD-6AC2exhibited a homeotropic alignment. After UV irradiation of the same sample, the schlieren texture due to a planar orientation was observed, and the texture was maintained even after 133 days. ThusD-6AC2can induce the stable planar alignment of NLC upon UV irradiation. Furthermore,D-6AC2could induce a planar homogeneous alignment by polarized UV light irradiation. [ABSTRACT FROM AUTHOR]

We present a new approach for the alignment process to orient liquid crystal (LC) molecules. The process consists of fabrication of a stamp composed of reactive mesogens (RMs), transfer of RM from the stamp onto polyimide (PI) layers, and LC device fabrication using the resulting RM/PI layers. The RM stamp was made anisotropic by a rubbing treatment, and this anisotropy was transferred to the PI layers via contact imprinting, leading to an achievement of uniform LC alignment. In addition, the pretilt angle of the LC molecules could be controlled by varying the content of homogeneous PI in the PI layers. We describe the effects of high pretilt angle upon the electro-optical (EO) characteristics of twisted-nematic (TN) cells based on the RM transfer film/blended PI layers. [ABSTRACT FROM AUTHOR]

We report the results of our studies on the optical and thermal properties of the mixture of 4-cyano-4′-octyloxybiphenyl (80CB) and N-Cetyl-N, N, N, trimethyl ammonium bromide (CTAB) + Glacial acetic acid (GAA), which exhibits a very interesting lower temperature reentrant nematic and smectic-A phases, sequentially when the specimen is cooled from its isotropic liquid phase. The different phases of these mixtures are identified using optical and microscopic techniques. The temperature variations of optical anisotropy, Ultrasonic velocity, molar compressibility, and adiabatic compressibility have been also discussed. [ABSTRACT FROM AUTHOR]

Calamitic luminophores are presented based on an elongated aryl-substituted coumarin core. The substitution pattern at terminal and lateral positions were systematically modified. The new compounds exhibit smectic C and/or nematic liquid crystalline phases. The chromophores show fluorescence in the blue spectral region. The benzopyranones are miscible with acrylate-substituted reactive nematic mesogens. Uniaxial orientation of the mixed systems was achieved by surface-assisted alignment on polyimide orientation layers. The film anisotropy was stabilised by subsequent photocrosslinking. The crosslinked oriented films display linear polarised photoluminescence upon isotropic excitation. [ABSTRACT FROM PUBLISHER]

This review focuses on two of our studied bent-core liquid crystals 2-methyl-3-[4-(4-octylbenzoyloxy)-benzylidene]-amino-benzoic acid 4-(4-dodecylphenylazo)-phenyl ester A131, and a shape-persistent fluorenone mesogen, F1a by means of temperature-dependent 13C NMR spectra and deuterium NMR spectra, respectively. Orientational order parameters, molecular packing, and/or conformations in the nematic phases or nematic glass can be extracted from the observed NMR spectra. These will be discussed in terms of certain motional models. In particular, F1a has been found to form a biaxial nematic glass. The derived orientational order parameters would put the biaxial system of phase symmetry lower than orthorhombic. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: A protocol for the preparation of a series of liquid crystals is presented, where the structures carry a central propyleneoxy motif carrying two vicinal threo-C–F bonds. The negative dielectric anisotropy (−Δɛ) of the resultant liquid crystals has been explored. The stereoelectronic relationship between the vicinal C–F bonds was anticipated to orientate the fluorine atoms gauche to each other when the propylene chain is extended. This is shown to be the case. This orientation of the C–F bonds generates a net dipole perpendicular to the molecular axis, a prerequisite for the design of dielectrically negative liquid crystals. However the molecules adopt a conformation where one C–F bond reinforces the net molecular dipole, and the other has a counter effect, thus the introduction of the motif has an almost neutral effect on dielectric anisotropy (Δɛ virt) of these candidate liquid crystals. However, introduction of the difluoro motif raises the melting points of the liquid crystals and increases their conformational rigidity. [Copyright &y& Elsevier]

Abstract: Study of the thermo-morfologic, thermotropic and thermo-optical properties of monomorphic nematic mesogen has been carried out. Temperature behavior of the mean the refractive index n, ordinary n o and extraordinary n e refractive indexes, and birefringence Δn have been investigated. The principal polarizabilities α 0 and α e , effective geometry parameter α eg , average polarizability α ave and polarizability anisotropy Δα were estimated. Peculiarities of the biphasic regions of the direct nematic mesophase–isotropic liquid and inverse isotropic liquid–nematic mesophase have been investigated. [Copyright &y& Elsevier]

We present experiments in which we use an electric field to switch between different configurations in the cellular patterns induced in a confined nematic liquid crystal by the contact with a surfactant monolayer that features lateral order and surface defects. By using different combinations of far-field alignment and mesogen dielectric anisotropy, we unravel the nature and stability of point defects and disclinations resulting from the hybrid boundary conditions. [ABSTRACT FROM AUTHOR]

Thiophene based calamitic mesogens are receiving paramount importance due to their applications in functional organic materials. The insertion of thiophene in the core unit favours a large change in mesophase characteristics as well as application properties in contrast to those mesogens with phenyl ring core alone. In this work, we report the structural as well as mesophase characterization of six mesogens which are built with a core of three phenyl rings and thiophene ring. The thiophene ring is placed at one end of the core and varied the other end with alkyl/alkoxy chains to investigate the mesophase characteristics. The molecular structures of representative mesogens are confirmed by means of FT-IR and Two-dimensional solution NMR techniques. An enantiotropic nematic phase is observed in all the cases as supported by HOPM and DSC techniques. The mesophase characteristics such as melting and clearing temperatures and phase stability are discussed. A dramatic increase in nematic phase stability for the synthesised mesogens is noticed in contrast to two phenyl ring based thiophene mesogens reported in literature. [ABSTRACT FROM PUBLISHER]

A new series of mesogenic compounds having a cholesteryl moiety has been synthesised by condensingp-amino benzoate of cholesterol and methoxy substituted 4-n-alkoxy cinnamoyl chlorides and their liquid crystalline properties has been studied. All the members of the series are enantiotropic and exhibit chiral nematic (N*) mesophase. The plot of transition temperatures versus number of carbon atoms in the alkoxy chain exhibits odd–even effect and falling tendency for N*–isotropic transition temperatures. The compounds exhibit oily streak textures that on slight disturbance change to the plane textures and show iridescent colours. High anisotropy, linearity and intermolecular hydrogen bonding confer rich mesomorphic properties on the system. Intermolecular hydrogen bonding arising from amide linkage can lead to supramolecular motifs. [ABSTRACT FROM AUTHOR]

The chiral, heliconical (twist-bend) nematic ground state is reported in an achiral, rigid, bent-core mesogen (UD68). Similar to the nematic twist-bend (/VTB) phase observed in bent molecular dimers, the NTB phase of UD68 forms macroscopic, smecticlike focal-conic textures and exhibits nanoscale, periodic modulation with no associated modulation of the electron density, i.e., without a detectable lamellar x-ray reflection peak. The NTB helical pitch is pTB~ 14 nm. When an electric field is applied normal to the helix axis, a weak electroclinic effect is observed, revealing 50-μm-scale left- and right-handed domains in a chiral conglomerate. [ABSTRACT FROM AUTHOR]

Liquid crystal elastomers (LCEs) are smart elastomers capable of a reversible shape change triggered by a stimulus such as heat or light. This change in shape is programmed into the material by orienting the mesogen molecules, often through the post-manufacturing alignment of the polymer chains by mechanical stretching. This method limits the possible orientations and necessitates a second curing step to lock the orientation in the structure. Direct ink writing allows for the curing of LCEs directly in an oriented state and for a fine control of the local orientation of the mesogens. The process parameters dictate the actuation and mechanical properties of the 4D-printed object, where time is the fourth dimension. We present in this paper a study of the influence of the printing speed and raster angle on the actuation strain and mechanical properties of the resulting LCE. Complex shape changes can be programmed into specimens that combine variations in printing angles and speeds. We printed two dimensional specimens actuating into helicoids and hinges. Results show the expected influence of printing speed on the level of orientation of the mesogens and on the actuation strain; that is faster printing equals more orientation and actuation strain. The change in raster angle demonstrates the immediate impact of incompatible strains in the structure, as the flat specimen (i.e. a printed rectangle of a couple of layers thick) actuates in a controlled 3D configuration. Finally, the hinge and helicoid specimens show the versatility of 4D-printed LCE systems, where the folding angle of the hinge or the pitch of the helicoid can be programmed through basic geometry, angle, and speed control at the printing stage. This transformative step in the preparation of LCE actuators opens the door to precise customization exploiting the mobility of mesogens on the polymer chains during printing and the flexibility of the direct ink writing process. [Display omitted] • Direct ink writing simultaneously orients and cures the liquid crystal elastomer. • We study the influence of printing speed and raster angle on actuation and mechanical properties. • Faster printing improves orientation and actuation strain. • Incompatible strains lead flat specimens to actuate in a controlled 3D configuration. • Hinge folding angle or helicoid pitch can be programmed through geometry, angle, and speed. [ABSTRACT FROM AUTHOR]

Photosensitive soft matter based upon guest-host liquid crystal systems was prepared by mixing azobenzene-containing mesogens with the nematic liquid crystal 4-butyl-cyclohexane carboxylic acid 4-pentyloxy-phenyl ester (CM80). Binary mixtures of the host CM80 with three azo-bonded compounds as UV-active dopants (guests) at a relatively small concentration of 1 wt.% were characterized by thermo-optical, dielectric, spectral and flexoelectric measurements. The study aimed to determine the mechanisms that result in variations of material parameters caused by light-driven molecular conformation change of the azo-dye guest molecules (the transition from rod-shaped trans isomers to bent-shaped cis isomers). [ABSTRACT FROM AUTHOR]

Three series of nematogens with a terminalp-nitrophenyl group linked with biphenyl groups via flexible spacers were synthesised and their transitional properties were studied by means of differential scanning calorimetry (DSC) and polarising microscopy (POM). The nematic–isotropic transition temperature and the associated entropy change showed an odd–even effect as the length of the spacers was varied, in which the even members exhibited higher values. Such an odd–even effect was in consistency with the feature of liquid crystal dimers and trimers. On the basis of these data, it seemed reasonable to assume that the terminalp-nitrophenyl group played a role of mesogen in the nematic liquid crystal. Thep-nitrophenyl group may work as a mesogen as a result of the interaction with the biphenyl mesogens. The mesogenic behaviour of the terminalp-nitrophenyl group is explained on the basis of neighbouring group effect. [ABSTRACT FROM AUTHOR]

Isothermal-isobaric(NPT) Monte-Carlo simulation has been used to investigate the nature of pair-correlations and ordering in a two-Dimensional system of soft ellipses with aspect ratio κ = 3 interacting via the Gay-Berne potential. The system is found to exhibit an isotropic phase (with exponential decay of orientational correlations) and a nematic phase (with algebraic decay of orientational correlations) as we suitably change temperature and pressure. The large distance decay exponent of the orientational correlations is found to converge around an universal value of 0.5 with the increase in pressure along an isotherm. The algebraic decay of orientational correlation in the low temperature phase shows that the nematic lacks true-long range orientational order. This has been substantiated by the system size dependence of the nematic order parameter. We have found the emergence of localized nematic patches separated by disclinations on increasing the pressure in the isotropic phase. No abrupt change is observed in pressure-density plot corresponding to the isotherms studied in this work. [ABSTRACT FROM AUTHOR]

We propose a fabrication method for a zero-pretilt nematic liquid crystal cell using UV-curable polymer. The zero pretilt angle can be obtained by UV curing of reactive mesogen monomers mixed with planar alignment material while a vertical electric field is applied to a liquid crystal cell assembled after the rubbing process. We demonstrate that the pretilt angle of a nematic liquid crystal cell can be decreased to 0.082° by employing the proposed method. [ABSTRACT FROM AUTHOR]

We propose a novel approach to achieve a homogeneous alignment of nematic liquid crystal (LC). Two bare substrates are rubbed in antiparallel direction and a mixture of LC and reactive mesogen (RM) is filled into the cell using capillary injection, and then UV is exposed after confirming the clear homogenous alignment. The cell shows an excellent dark state and stable electro-optic on/off switching in the IPS cell, which proves polymerized RM on surfaces plays role of alignment layer. Proposed fabrication method has several advantages such as simple process and low cost for IPS cell because alignment layer as well as the coating process is not required. [ABSTRACT FROM AUTHOR]