Chiral Nematic Liquid Crystal Research Articles

The Missing Relationship between the Miscibility of Chiral Dopants and the Microscopic Dynamics of Solvent Liquid Crystals: A Molecular Dynamics Study

Nematic liquid crystals (LCs) are known to undergo a phase transition to chiral nematic LCs possessing helices upon doping with enantiomeric molecules known as chiral dopants. The relationship between the helical pitch (p), the molar fraction (x), and the power of the chiral dopant to induce a helix in a nematic solvent (βM) is expressed as p=1/(x·βM). The helical pitch is easily controlled by the concentration of the chiral dopant when the dopant molecule is miscible with the host nematic LC. However, it has not yet been clarified what the miscibility of the chiral dopant molecules with the nematic LCs depends. Therefore, we performed all-atom molecular dynamics (MD) simulations for the system composed of both Δ and Λ isomers of a chiral dopant molecule dispersed in a nematic LC and investigated the relationship between the microdynamics of the chiral molecules and their miscibility with the nematic solvent. The miscibility of the chiral dopant molecules with the LC solvent was found to correlate with the diffusion coefficient of the LC solvent. In the system where the chiral dopant molecules with high miscibility were added, the diffusion coefficient of the LC solvents was comparable to that of the system in which the chiral molecule was not doped. Furthermore, it was confirmed that more elongated chiral dopants were more miscible with the nematic solvent consisting of calamitic molecules, and that these dopant molecules did not have a significant effect on the diffusion behavior of the LC molecules.

Liquid-crystalline assembly of spherical cellulose nanocrystals

Rod-shaped cellulose nanocrystals (CNCs), also called cellulose nanorods (CNRs), possess anisotropic properties that allow for their self-organization into chiral nematic liquid crystals. Interestingly, spherical cellulose nanocrystals (cellulose nanospheres, CNSs) have also been shown to form a chiral liquid-crystalline phase in recent years. Herein, to understand how the similar assembly takes places as particle dimension changes, the organization features of CNSs were investigated. Results of this study demonstrate that above a critical concentration in suspension, CNSs organize into a liquid-crystal phase consisting of periodically parallel-aligned layer structures. This structure persists after suspension drying. In comparison with CNRs, the alignment of CNSs exhibits a shorter layer distance, lower order degree, and weaker long-range orientation. To explain the early stages of tactoid formation, a “caterpillar-like” model was proposed, which was captured by freezing the CNS suspension in an intermediate aggregation state. This structure serves as the fundamental unit for further liquid-crystal assembly.

Photonic Bandgap and Excitation Wavelength Modulated Multicolor Upconverted Circularly Polarized Luminescence in Liquid Crystal Microcapsule

AbstractUpconverted circularly polarized luminescence (UC‐CPL) which is coined by integrating two concepts of photon upconversion and circularly polarized luminescence, has aroused enormous attention from scientists owing to the great performance and potential applications in various fields. To date, although various types of UC‐CPL systems are reported, constructing a UC‐CPL system with multicolor emission remains a big challenge. In this work, by incorporating lanthanide‐doped upconversion nanoparticles (UCNPs) into chiral nematic liquid crystal (N*LC), multicolor UC‐CPL emission can be realized upon two kinds of modulations: the regulation of photonic bandgap (PBG) and adjustment of excitation wavelength of the doped UCNPs. More importantly, this kind of multicolor UC‐CPL system can be used as internal materials for constructing polymer‐shell microcapsules. The PBG effect can still be well preserved in the microcapsules, providing a kind of easy processable luminescent material with multicolor UC‐CPL properties, which can be used as an advanced anti‐counterfeiting material.

Emergence of disordered branching patterns in confined chiral nematic liquid crystals

Spatial branching processes are ubiquitous in nature, yet the mechanisms that drive their growth may vary significantly from one system to another. In soft matter physics, chiral nematic liquid crystals provide a controlled setting to study the emergence and growth dynamic of disordered branching patterns. Via an appropriate forcing, a cholesteric phase may nucleate in a chiral nematic liquid crystal, which self-organizes into an extended branching pattern. It is known that branching events take place when the rounded tips of cholesteric fingers swell, become unstable, and split into two new cholesteric tips. The origin of this interfacial instability and the mechanisms that drive the large-scale spatial organization of these cholesteric patterns remain unclear. In this work, we investigate experimentally the spatial and temporal organization of thermally driven branching patterns in chiral nematic liquid crystal cells. We describe the observations through a mean-field model and find that chirality is responsible for the creation of fingers, regulates their interactions, and controls the tip-splitting process. Furthermore, we show that the complex dynamics of the cholesteric pattern behaves as a probabilistic process of branching and inhibition of chiral tips that drives the large-scale topological organization. Our theoretical findings are in good agreement with the experimental observations.

Synthesis And Structural Feasibility Of Photonic Materials

Aim: Studying the optical-thermal dependence of liquid crystal based on the quantity data of image texture is essential to get more information accurately Background: In this research, the optical-thermal dependence of chiral nematic liquid crystals ink sample was investigated based on the sample's texture and colour changes at various temperatures. Objective: The structural and optical characteristics of ZnO thin films are investigated in this study. While spinning at 4000 rpm for 30 seconds at room temperature, the zinc oxide solution was spun onto a pre-cleaned, glass substrate, creating the desired layer thickness. method: This was followed by annealing at 150°C-600°C in 50°C steps, which was carried out on the samples. An ultraviolet-visible spectrophotometer and a scanning electron microscope were used to analyse the optical properties of this thin coating. Method: This was followed by annealing at 150°C-600°C in 50°C steps, which was carried out on the samples. An ultraviolet-visible spectrophotometer and a scanning electron microscope were used to analyse the optical properties of this thin coating. Result: Zinc oxide's optical band gap was determined by measuring its optical transmittance, reflectance, and absorbance. Photonic crystals can exhibit relevant optical properties when transmitting or reflecting a light beam. conclusion: In particular, in a two-dimensional photonic crystal, the reflective properties can be of interest and consequently optimized for different technological applications such as tuneable laser cavities, photovoltaic solar systems, and selective high reflection mirrors, among many others. Conclusion: In particular, in a two-dimensional photonic crystal, the reflective properties can be of interest and consequently optimized for different technological applications such as tuneable laser cavities, photovoltaic solar systems, and selective high-reflection mirrors, among many others.

Local chiral inversion of chiral nematic liquid crystals in cylinders.

On the basis of Landau-de Gennes theory and the finite-difference iterative method, the autonomic modulation of chiral inversion in a cylindrical cavity with degenerate planar anchoring is investigated. Under the applied helical twisting power (inversely related to the pitch P), a chiral inversion can be achieved due to the nonplanar geometry effect, and the inversion capacity rises with the increase of the helical twisting power. The combined effect of the saddle-splay K_{24} contribution (corresponding to the L_{24} term in Landau-de Gennes theory) and the helical twisting power are analyzed. It is found that the chiral inversion is more strongly modulated on the condition that the chirality of spontaneous twist is opposite to that of applied helical twisting power. Further, larger values of K_{24} will induce larger modulation of the twist degree and smaller modulation of the inverted region. The autonomic modulation of chiral inversion shows great potential for chiral nematic liquid crystal materials to be used in smart devices, such as light-controlled switches and nanoparticle transporters.

Emergence of disordered branching patterns in confined chiral nematic liquid crystals

Emergence of disordered branching patterns in confined chiral nematic liquid crystals

Monte Carlo simulations of chiral and achiral nematic droplets: thermal quenches and role of the elastic constants

ABSTRACTWe used Monte Carlo simulations with an elastically anisotropic pairwise potential to simulate the equilibrium structure of chiral and achiral nematic liquid crystals in spherical confinement under perpendicular and tangential strong anchoring. The stable structures are obtained by a quenching process, where the temperature is a parameter of the system. We calculate and map the distribution of elastic energy corresponding to splay, twist, and bend. Furthermore, we study the effect of changing the ratio of the elastic constants for achiral and low chirality droplets and found a diverse scenario of possible structures. The method described here allows the introduction of temperature and elastic anisotropy naturally within its framework. It is simpler to implement and faster to execute than the Landau-de Gennes (LdG) method used for simulating liquid crystal droplets.

Bone ECM-inspired biomineralization chitin whisker liquid crystal hydrogels for bone regeneration

As a particular cell niche, natural bone extracellular matrix (ECM) is an organic-inorganic composite material formed by mineralization of liquid crystal (LC) collagen fiber network. However, designing bone repair materials that highly imitate the LC characteristic and composite components of natural bone ECM is a great challenge. Here, we report a novel kind of bone ECM-inspired biomineralization chitin whisker LC hydrogels. First, photocurable chitin whisker LC hydrogels with bone ECM-like chiral nematic LC state and viscoelasticity are created. Next, biomineralization, guided by LC hydrogels, is carried out to truly mimic the mineralization process of natural bone, so as to obtain the organic-inorganic composite materials with bone ECM-like microenvironment. The chitin whisker LC hydrogels exhibit superior biomineralization, protein adsorption and osteogenesis ability, more importantly, LC hydrogel with negatively charged –COOH groups is more conducive to biomineralization and shows more desirable osteogenic activity than that with positively charged –NH2 groups. Notably, compared with the pristine LC hydrogels, the biomineralization LC hydrogels display more favorable osteogenesis ability due to their bone ECM-like LC texture and bone-like hydroxyapatite. This study opens an avenue toward the design of bone ECM-inspired biomineralization chitin whisker LC hydrogels for bone regeneration.

Cellulose: A Review of Water Interactions, Applications in Composites, and Water Treatment.

Cellulose is known to interact well with water, but is insoluble in it. Many polysaccharides such as cellulose are known to have significant hydrogen bond networks joining the molecular chains, and yet they are recalcitrant to aqueous solvents. This review charts the interaction of cellulose with water but with emphasis on the formation of both natural and synthetic fiber composites. Covering studies concerning the interaction of water with wood, the biosynthesis of cellulose in the cell wall, to its dispersion in aqueous suspensions and ultimately in water filtration and fiber-based composite materials this review explores water-cellulose interactions and how they can be exploited for synthetic and natural composites. The suggestion that cellulose is amphiphilic is critically reviewed, with relevance to its processing. Building on this, progress made in using various charged and modified forms of nanocellulose to stabilize oil-water emulsions is addressed. The role of water in the aqueous formation of chiral nematic liquid crystals, and subsequently when dried into composite films is covered. The review will also address the use of cellulose as an aid to water filtration as one area where interactions can be used effectively to prosper human life.

Theory of elastic interaction between axially symmetric 3D skyrmions in confined chiral nematic liquid crystals and in skyrmion bags

ABSTRACT We study axially symmetrical 3D skyrmionic particles (torons, Hopfions) in a thin homeotropic cell filled with a cholesteric liquid crystal. We show that a small 3D skyrmion asymptotically can be presented as a particle with six multipole moments. In this case, the odd moments – dipole, octupole and the fifth-order moments – are helicoidal moments, generated by chirality. And even moments – quadrupole, hexadecapole and sixth order moments – have the usual form, as colloidal particles in nematics. Thus, we find the exact analytical solution for the far field director configuration around the 3D skyrmion and the exact analytical expression for the elastic interaction potential between 3D skyrmions in a homeotropic cell with thickness . We show that it has an exponential decay length equal . The comparison with the experiment allows us to recover approximately one set of multipole coefficients for the small 3D skyrmion. We also describe the expansion of the skyrmion bag analytically depending on the number of anti-skyrmions in it and obtain an agreement with the experiment. Along the way, we determined the director field and the elastic interaction potential betweenchiral axially symmetric colloidal particles in the unlimited nematic and in the homeotropic cell, taking into account higher order elastic terms.

Chiral nematic liquid crystal organization of natural polymer nanocrystals

ABSTRACT One-dimensional nanocrystals with high-aspect ratio from natural polymers such as cellulose nanocrystals are attractive due to their anisotropic dimensions, versatile surface chemistry and ability to form lyotropic liquid crystalline (LC) phase in aqueous media. Most importantly, those anisotropic natural materials preserve their LC ordering in solid films under slow drying at ambient conditions. The resulting organised films with ‘frozen’ chiral nematic helicoidal morphology show unique optical properties such as selective light reflection, high optical birefringence, selective circular polarisation, along with enhanced mechanical performance, e.g. high ultimate strength, toughness and stretchability. Additionally, those films are lightweight, and potentially sustainable and biodegradable. Here we briefly overview recent work from our group on the chiral nematic organisation in LC suspensions and in thin films of cellulose nanocrystals and cellulose nanofibers obtained under diverse interparticle interactions, confined drying conditions, and external magnetic field.

Heads or tails: investigating the effects of amphiphile features on the distortion of chiral nematic liquid crystal droplets.

Liquid crystal-based sensing has fast become a growing field, harnessing the sensitivity of liquid crystals to their surroundings to provide information about the analytes present, including surface-active amphiphiles such as biological lipids. Amphiphiles can impart ordering to a liquid crystal and, in the case of chiral nematic liquid crystals (CLCs), distort the helical texture. The cause and degree to which this distortion occurs is not fully clear. In this work, the effects of different amphiphiles on the final colour textures as well as the pitch of chiral nematic liquid crystals are investigated. We find that the tails of amphiphiles and their orientation play a more important role in determining the final distortions of the liquid crystal by the direct interactions they have with the host, whereas the headgroups do not play a significant role in affecting these distortions. Our findings may find implications in designing CLC-based biosensors, where the tails will likely have more impact on the CLC response, while the headgroups will remain available for further functionalization without having significant effects on the signal readout.

Temperature reconfigurable skyrmionic solitons in cholesteric liquid crystals.

In this work, a reversible transformation between torons and cholesteric fingers is realized by continuously changing the pitch through temperature variation of the chiral nematic liquid crystal twist inversion system. By decreasing the pitch, the torons act as seeds from which cholesteric fingers gradually grow. By increasing the pitch, the cholesteric fingers gradually shorten and transform back to the initial state. We find that although the morphology of the torons is severely deformed and cannot be distinguished during the heating-cooling loops, the torons are very well topologically protected and can hardly be destroyed.

Dynamics of coreless defects during winding up transitions in confined chiral nematic liquid crystals.

Twist-coupled elastic deformations are ubiquitous and in the limelight of interest for next-generation self-shaping materials. Here, we describe how twist dynamics under fixed anchoring lead to bend deformation and defect dynamics in a field-unwound chiral liquid crystal material. We use the Q-tensor dynamics under the Landau-de Gennes formalism in a finite-element mesh to explore the texture pathways from the unwound (homeotropic) to the helical planar structure. Our simulations describe well previously reported experiments and confirm that the process occurs by forming pairs of coreless defects that interact with each other and create quadrupolar structures called Lehmann clusters. The dynamics and coarsening of dipoles and quadrupoles of defects are described. This numerical study describes the full dynamics, which has been sought for several years.

Optical Imaging and Analytical Design of Localized Topological Structures in Chiral Liquid Crystals

We combine numerical modeling and analytical design techniques to study several of the most common localized topological structures in frustrated chiral nematic liquid crystal cells. An energy minimization procedure is applied to the lattice model to simulate the director field distributions. These distributions are also approximated using the suitably designed analytical ansatz. We present both simulated and approximated results for optical polarizing microscopy textures and different visualizations of director field structure such as distributions of the azimuthal director angle and isolines for the normal component of the director in coordinate planes. The ansatz correctly mimicked the geometry and optical properties of the solitonic structures under consideration.

Photocurable liquid crystal hydrogels with different chargeability and tunable viscoelasticity based on chitin whiskers

We develop a kind of photocurable liquid crystal hydrogels with bone extracellular matrix (ECM)-like liquid crystal state and viscoelasticity, as well as different chargeability. First, positively charged chitin whiskers (CHWs) and negatively charged maleic anhydride chitin whiskers (mCHWs) were prepared, which further self-assemble to form chiral nematic liquid crystals under ultrasonic treatment, respectively. Subsequently, poly (ethylene glycol) diacrylate (PEGDA) and photo initiator were added, and then two kinds of liquid crystal hydrogels with bone ECM-like viscoelasticity and different chargeability were prepared under ultraviolet (UV) irradiation. Benefiting from the bone ECM-like liquid crystal state and viscoelasticity, the prepared liquid crystal hydrogels exhibit remarkable cell affinity and osteogenic ability. Moreover, the liquid crystal hydrogel with negatively charged mCHWs is more favorable for cell adhesion, spreading and osteogenic differentiation than that with positively charged CHWs. This work provides a promising strategy to prepare the hydrogels with bone ECM-like liquid crystal properties and viscoelasticity for bone repair.

Printed Structurally Colored Cellulose Sensors and Displays

AbstractHydroxypropyl cellulose (HPC) is a commercially available and biodegradable cellulose derivative, which is known to self‐assemble into chiral nematic liquid crystal phases in water. These features, including liquid crystal‐induced selective reflections in the visible range, make HPC an ideal biopolymer host material for dynamic structural color‐shifting materials. Herein, HPC is used as a starting matrix material and found that, by adding carbon nanotubes (CNT) to an aqueous dispersion of HPC, the color saturation can be improved without influencing the structural color formation and simultaneously conferring electrical conductivity to the material. Additionally, up to 0.4 wt% of cellulose nanofibrils (CNF) can be added to control and tune the rheological properties of the suspension allowing for 3D printability while also maintaining the structural colors. The HPC‐CNT‐CNF printed composite materials show application for flexible color‐changing devices in the form of a dual readout optical and resistive strain sensor and is used as the active material in a dynamic seven‐segment color display. This multipurpose color‐changing material has the potential to be used in the creation of eco‐friendly visual intelligent devices and biodegradable user interfaces and, as such, contributes to the advancement of the field of sustainable and green electronics.

Rapid and Label-Free Methanol Identification in Alcoholic Beverages Utilizing a Textile Grid Impregnated with Chiral Nematic Liquid Crystals.

Methanol contamination of alcoholic drinks can lead to severe health problems for human beings including poisoning, headache, blindness, and even death. Therefore, having access to a simple and inexpensive way for monitoring beverages is vital. Herein, a portable, low cost, and easy to use sensor is fabricated based on the exploitation of chiral nematic liquid crystals (CLCs) and a textile grid for detection of methanol in two distinct alcoholic beverages: red wine and vodka. The working principle of the sensor relies on the reorientation of the liquid crystal molecules upon exposure to the contaminated alcoholic beverages with different concentrations of methanol (0, 2, 4, and 6 wt %) and the changes in the observed colorful textures of the CLCs as well as the intensity of the output light. The proposed sensor is label free and rapid.

Stable hazy states by electrohydrodynamic convection of ultraviolet-treated chiral nematic liquid crystal

In this paper, we show that electrohydrodynamic convection of ultraviolet (UV)-treated chiral nematic liquid crystals (CNLCs) generates stable foggy states. UV-irradiation produces relatively heavier and larger molecular ions at CNLC mixture, which activates electroconvection, and leads to easily dynamic scattering mode (DSM) with strong turbulence. Chirality of LC combined with the DSM builds two stable states (planar state and focal conic state) more strongly, unlike the conventional method generating the two states in the CNLCs. The molecular ion effect enables state conversion to a much lower switching voltage than that of the conventional cholesteric devices. The focal conic state connected to DSM2 exhibits a stable deep hazy state, the mixed state combined with DSM1 displays a stable weak hazy state, and the planar state activated in a particular frequency region creates a stable and very clear transparent state due to the chiral pitch of the infrared region. Therefore, a smart window with the tri-stable-hazy state specialized in low power consumption can be realized. The tri-stable-hazy state device also generates various hazy states according to the applied voltage; thus, it can provide a proper indoor temperature for users. Furthermore, a stable planar state with a chiral pitch designed in the infrared region may save energy through selective reflection of infrared rays from the sunlight in the summer. The proposed technology is suitable for commercial use in the next-generation smart window.