Chiral Nematic Liquid Crystalline Research Articles

Investigating the phase behaviour of binary suspensions of cellulose nanocrystals and montmorillonite with nonlinear rheology, SAXS and polarized optical microscopy

Using microscopy imaging techniques, X-ray scattering, and nonlinear rheological measurements, we have examined microstructural changes, and phase behavior of cellulose nanocrystals (CNC)/montmorillonite (MMT) composite colloidal systems. Fourier-transform (FT) rheology-stress decomposition methods, Lissajous-Bowditch plots, and other techniques are used to both qualitatively and quantitatively determine the various phases that the suspensions exhibit. In the MAOS (medium amplitude oscillatory shear) region, multiple scaling regions, as well as quadratic scaling regions are obtained. The dependence of the normalized third relative intensity (I3/1) values on angular frequency (ω) also provided new insights into how nonlinear parameters depend on the various CNC/MMT phases. These findings allow us to differentiate various phases exhibited by the composite system, including the isotropic, biphasic, and chiral nematic liquid crystalline (LC) phases. The CNC/MMT nanocomposite system exhibits a variety of liquid crystalline phases, which may contribute to improved mechanical properties for the system, including increased mixture strength, stiffness, and toughness because of the particle alignment in the LC phase. Additionally, the field of optics and photonics may find use for this nanocomposite system in the fabrication of sensors, polarizers, and optical films; energy storage applications where the aligned structures facilitate ion transport; and the formulation of paints and coatings where the strain stiffening and shear thinning behavior of the CNC/MMT composite system are critical.

3D printing of responsive chiral photonic nanostructures

Finely controlled flow forces in extrusion-based additive manufacturing can be exploited to program the self-assembly of malleable nanostructures in soft materials by integrating bottom-up design into a top-down processing approach. Here, we leverage the processing parameters offered by direct ink-writing (DIW) to reconfigure the photonic chiral nematic liquid crystalline phase in hydroxypropyl cellulose (HPC) solutions prior to deposition on the writing substrate to direct structural evolution from a particular initial condition. Moreover, we incorporate polyethylene glycol (PEG) into iridescent HPC inks to form a physically cross-linked network capable of inducing kinetic arrest of the cholesteric/chiral pitch at length scales that selectively reflect light throughout the visible spectrum. Based on thorough rheological measurements, we have found that printing the chiral inks at a shear rate where HPC molecules adopt pseudonematic state results in uniform chiral recovery following flow cessation and enhanced optical properties in the solid state. Printing chiral inks at high shear rates, on the other hand, shifts the monochromatic appearance of the extruded filaments to a highly angle-dependent state, suggesting a preferred orientation of the chiral domains. The optical response of these filaments when exposed to mechanical deformation can be used in the development of optical sensors.

Novel graphene oxide derivatives and its effect in broad-band reflectors

ABSTRACT n-Octylyamine (CA) was chemically grafted onto carboxylic groups of graphene oxide (GO) via amidation reaction. The resultant modified GO sheets (GO-CA) were easily redispersed in common organic solvents or liquid crystals (LCs), facilitating the structure characterisation and the device fabrication by solution processing. Broadband reflectors could be obtained by doping different contents of GO-CA nanosheets into chiral nematic liquid crystalline (N*-LCs) media to a photo-polymerisation. Experimental results showed that both the bandwidth of the reflection spectra and the location of the reflection band of the GO-CA-doped composite films were better than the N*-LCs sample without GO-CA. Effects of polymerisation temperatures and doped contents of GO-CA on the broadband reflection of N*-LC composite films were investigated.

Janus Oligomers Demonstrating Full‐Spectrum Visible Light Reflection and Tunable Photoluminescence towards Dual‐Mode Dynamic Anti‐Counterfeiting

AbstractStimulus‐responsive multimodal optical materials demonstrating tunable optical behaviors possess significant application in optoelectronic materials and devices. Introducing fluorescent elements into liquid crystal structures is a common strategy. The design of hybrid optical structure at molecular level is seldom reported. Herein, novel Janus oligomers (JOs) combining the chiral nematic liquid crystalline (CNLC) units and the photoluminescent (PL) units on organosilicon oligomers by molecular grafting are proposed. The as‐prepared JOs display brilliant visible light reflection originating from the chiral arrangement of the CNLC segments. The discrete pyrene chromogenic segments in the CNLC matrix enable the quantum yield and PL lifetime of JOs to be up to 38.58% and 68.45 ns. Furthermore, the JOs present dual‐mode thermochromic performances, the blue‐shift reflection across the full‐spectrum visible light region, and the highly sensitive PL evolution. The JOs can be manufactured into dynamic anti‐counterfeiting patterns with fast and reversible response by screen printing. The Janus optical structure enabled by chemically coupling different optical elements at the molecular level provides a templated strategy to create the next generation of intelligent hybrid optical materials.

Retrieving the Coassembly Pathway of Composite Cellulose Nanocrystal Photonic Films from their Angular Optical Response.

Aqueous suspensions of cellulose nanocrystals (CNCs) are known to self-assemble into a chiral nematic liquid crystalline phase, leading to solid-state nanostructured colored films upon solvent evaporation, even in the presence of templating agents. The angular optical response of these structures, and therefore their visual appearance, are completely determined by the spatial arrangement of the CNCs when the drying suspension undergoes a transition from a flowing and liquid crystalline state to a kinetically arrested state. Here, it is demonstrated how the angular response of the final film allows for retrieval of key physical properties and the chemical composition of the suspension at the onset of the kinetic arrest, thus capturing a snapshot of the past. To illustrate this methodology, a dynamically evolving sol-gel coassembly process is investigated by adding various amounts of organosilica precursor, namely, 1,2-bis(trimethoxysilyl)ethane. The influence of organosilica condensation on the kinetic arrest can be tracked and thus explains the angular response of the resulting films. The a posteriori and in situ approach is general; it can be applied to a variety of additives in CNC-based films and it allows access to key rheological information of the suspension without using any dedicated rheological technique.

Self‐Assembly of Chiral Nematic Liquid Crystalline Phases of AgNR@SiO2@Cysteine@CsPbBr3 Hybrid Nanorods with Plasmon‐Dependent Photoluminescence

AbstractThe direct synthesis of a chiral nematic liquid crystalline phase of AgNR@SiO2@cysteine@CsPbBr3 hybrid nanorods (HNRs) is reported. The circular dichroism spectra can be divided into three components: (1) the interband absorption–enhanced optical activity of structural arrangement of cysteine (cys) molecules, 200–320 nm, (2) the chiral nematic liquid crystalline arrangement of the Ag nanorods (AgNRs), 350–450 nm, and (3) the exciton adsorption edge of the perovskite, 500–550 nm. The polarizing optical microscope images indicate that the chiroptical response of perovskite arises from chiral nematic crystalline arrangement rather than cys‐induced electronic coupling between a chiral ligand and otherwise achiral perovskite quantum dots (QDs). The luminescent intensity of CsPbBr3 QDs in AgNR@SiO2@cys@CsPbBr3 HNRs is boosted 87‐fold due to the local surface plasmon resonance field enhancement effect. Furthermore, the high‐performance green light emitting diode is constructed employing AgNR@SiO2@cys@CsPbBr3 complexes, which exhibit excellent luminescent properties. This work contributes insights into structure–property relationships and this strategy promisingly provides guidance for the other inorganic chiral semiconductor suprastructures.

Hybrid Nanocomposites for 3D Optics: Using Interpolymer Complexes with Cellulose Nanocrystals.

Manipulation of optical paths by three-dimensional (3D) integrated optics with customized stacked building blocks has gained considerable attention. Herein, we present functional thin films with assembly ability for 3D integrated optics based on nanocomposites made of cellulose nanocrystals (CNCs) embedded in hydrogen-bonded (H-bonded) interpolymer complexes (IPCs). We selected H-bonded IPC poly(ethylene oxide) and neutralized poly(acrylic acid) to render films assembly ability without undesired interplay with charge distribution in CNCs. The CNCs can form a stable chiral nematic liquid crystalline phase with long-range orientational order and helical organization. The resulting nanocomposites are characterized with a high elastic modulus of 8.8 GPa and an adhesion strength of 1.35 MPa through reversible intermolecular interactions at the contact interface upon exposure to acidic vapor. Instead, simply stacked into 3D optics, these functional thin films serve as a facile material for providing a conceptually simple approach to assemble 3D integrated optics with different liquid crystalline orderings to manipulate the light polarization state.

Helicity Control of Supramolecular Gel Fibers Consisting of an Achiral NiII Complex in a Chiral Nematic Solvent.

The supramolecular chirality of aggregates consisting of achiral trans-bis(salicylaldiminato)NiII complex 1 bearing long alkyl chains can be generated and controlled precisely in a chiral nematic liquid-crystalline (LC) solvent, whereas the complex naturally forms achiral gel fibers in achiral nematic LC solvents and crystals in nonmesogenic solvents. The direction and intensity of the helicity of the gel fibers of 1 in the LC gel state can be adjusted by means of the nature of the helical twisting and the concentration of the chiral dopants. Helicity control was precisely detected in the circular dichroism (CD) spectra of LC gels and by direct SEM observation of the dried gel fibers. XRD analysis revealed that the flexibility of the herringbone-based lamellar alignment of this complex is the key to the LC-specific gelation and helicity control of the gel fibers.

TiO2 nanorod arrays induced broad-band reflection in chiral nematic liquid crystals with photo-polymerization network

ABSTRACTA series of TiO2 nanorod arrays were obtained by hydrothermal reaction, then the morphologies were characterized and analysed. In the light polymerization condition, different morphologies of TiO2 nanorod arrays and chiral nematic liquid crystalline (N*-LCs) media were combined to prepare broad-band reflectors. By adjusting the length and interval size of the TiO2 nanorod arrays, the reflection spectra and the positions of the reflected spectrum and the reflected bandwidth can be controlled accordingly. As a result, the effect of polymerization temperatures and morphologies of TiO2 nanorod arrays on the broad-band reflection in the N*-LC composite system has been investigated. Potential applications of the composite were related to brightness enhancement films, bandwidth-controllable reflective polarizers and near-infrared light blocking films.

Novel universality classes in ferroelectric liquid crystals

Starting from a Langevin formulation of a thermally perturbed nonlinear elastic model of the ferroelectric smectic-C* (SmC*) liquid crystals in the presence of an electric field, this article characterizes the hitherto unexplored dynamical phase transition from a thermo-electrically forced ferroelectric SmC* phase to a chiral nematic liquid crystalline phase and vice versa. The theoretical analysis is based on a combination of dynamic renormalization (DRG) and numerical simulation of the emergent model. While the DRG architecture predicts a generic transition to the Kardar-Parisi-Zhang (KPZ) universality class at dynamic equilibrium, in agreement with recent experiments, the numerical simulations of the model show simultaneous existence of two phases, one a subdiffusive (SD) phase characterized by a dynamical exponent value of 1, and the other a KPZ phase, characterized by a dynamical exponent value of 1.5. The SD phase flows over to the KPZ phase with increased external forcing, offering a new universality paradigm, hitherto unexplored in the context of ferroelectric liquid crystals.

Entropy-driven self-assembly of chiral nematic liquid crystalline phases of AgNR@Cu2O hyper branched coaxial nanorods and thickness-dependent handedness transition

The chiral nematic liquid crystalline phase (CNLCP) of noble metal nanorods induces a strong chiroptical response due to their intrinsic physical and chemical properties. Here, we demonstrate that the formation of CNLCP of Ag nanorods (AgNRs) originates from their bent-shape and is the result of purely entropic effects. The chirality of the liquid crystalline phase of AgNR@Cu2O hyper branched coaxial nanorods (HBCNRs) can be switched from left-handed to right-handed by increasing Cu2O thickness. It is proposed that the increase of coating thickness decreases the curvature of nanorods, which induces variation of the twist constant (K2) and bend elastic constant (K3). The increased thickness also changes the direction of director with respect to the helical axis. In addition, hydrogen bonds can break the CNLCP, which can be attributed to their stronger effection compared to van der Waals forces and electrostatic interactions. In contrast to the variation of coating thickness, the surface morphology, constituents of the hybrid building blocks and polarity of the solvents do not play important roles in the handedness transition of the liquid crystalline phase. Furthermore, the results presented here give insight into the structure–property relationship and our strategy provides guidance for the synthesis of other inorganic chiral suprastructures driven by entropic effects.

Synthesis and mesomorphism of modified 2,5-Di(4-dodecoxyphen-1-yl)-c-cyclopentene-pyridines

ABSTRACTHerein, we report on a new series of mesomorphic compounds synthesised by directional functionalisation of 2,5-di(4-dodecoxyphen-1-yl-c-cyclopentene-pyridine) on the c-cyclopentene moiety. The first functionalisation of the starting compound gave rise to a racemic product modified with a hydroxyl group on the fused cyclopentene ring. Further oxidation of this alcohol to a prochiral ketone and subsequent enantioselective reduction back to the alcohol afforded a new chiral alcohol. Further, the hydroxyl group of the chiral alcohol could be substituted by fluorine in a SN2 reaction, leading to a chiral compound with enantiomeric excess (ee) of 66% and chiral nematic liquid-crystalline (LC) phase.

Polarized Phosphorescence of Isotropic and Metal‐Based Clustomesogens Dispersed into Chiral Nematic Liquid Crystalline Films

Polarized Phosphorescence of Isotropic and Metal‐Based Clustomesogens Dispersed into Chiral Nematic Liquid Crystalline Films

Synthesis and Characterization of a Series of Cholesterol-Based Liquid Crystalline Dimers with a Chiral (-)- Menthyl Terminal Group

A novel series of cholesterol-based liquid crystalline (LC) dimers with a menthyl terminal group in the biphenyl base side have been synthesized. The chemical structures and LC properties of this series of compounds are characterized by FT-IR, 1H-NMR, elemental analysis, hot-stage coupled polarizing microscopy and differential scanning calorimetry. All the dimers exhibit enantiotropic mesophases. These dimesogenic compounds with a short spacer are chiral nematic LCs, while with long spacers, they are SmA and chiral nematic LCs. Some of these LC dimers exhibit iridescent colors in their chial nematic (N*) states.

Graphene Oxide Modified with Mesogenic Groups and Its Effect in Broad‐Band Reflectors

The NH2 -terminated mesogenic group 4-(6-amine-hexyloxy)-4*-cyan-biphenyl is chemically grafted onto the carboxylic groups of graphene oxide (GO) through an amidation reaction. The resultant mesogenic-group-modified GO sheets (GO-LC) are redispersed easily in common organic solvents, facilitating the structure characterization and device fabrication by solution processing. Broad-band reflectors are obtained by doping different contents of GO-LC nanosheets into chiral nematic liquid crystalline (N*-LCs) media with a photopolymerization process. The experimental results show that both the bandwidth of the reflection spectrum and the location of the reflection band of the GO-LC-doped composite films are better than those of the N*-LCs sample without GO-LC doping. The effects of polymerization temperature and amount of GO-LC dopant on the broad-band reflection of the N*-LC composite films are investigated.

3c16 Lyotropic Chiral Nematic Liquid Crystalline Di-substituted Polyacetylene Derivatives that exhibit Circularly Polarized Luminescence

3c16 Lyotropic Chiral Nematic Liquid Crystalline Di-substituted Polyacetylene Derivatives that exhibit Circularly Polarized Luminescence

Lyotropic Chiral Nematic Liquid Crystalline Aliphatic Conjugated Polymers Based on Disubstituted Polyacetylene Derivatives That Exhibit High Dissymmetry Factors in Circularly Polarized Luminescence

We synthesized disubstituted liquid crystalline polyacetylene (diLCPA) derivatives bearing 4-nonyloxy phenyl groups with lyotropic and thermotropic LC behavior. The poly(diphenylacetylene) main chain structure of the diLCPAs and the chirality induced with either chiral moieties or chiral dopants allow the formation of a highly ordered lyotropic N*-LC phase. Circular dichroism (CD) spectra of the diLCPAs imply that one-handed intrachain helical structures are formed in solution, while interchain helical π-stacking between the polymer main chains are formed in cast film and in the N*-LC state. Absorption dissymmetry factors (g(abs)) in the N*-LC state show values on the order of 10(-1). The N*-LC state facilitates the formation of helically π-stacked structures with a high degree of helical ordering of the diLCPA and is indispensable for the generation of circularly polarized luminescence (CPL) with high emission dissymmetry factors (g(em)) on the order of 10(-1). To the best of our knowledge, this is the highest reported value of CPL achieved for aliphatic, conjugated polymers. As an alternative to the thermotropic N*-LC phase, we have found that the lyotropic N*-LC phase of diLCPA could be promising materials possessing CPL functionality for use in next-generation π-conjugated organic optoelectronic devices, displays, and sensors.

Influence of a Change in Helical Twisting Power of Photoresponsive Chiral Dopants on Rotational Manipulation of Micro‐Objects on the Surface of Chiral Nematic Liquid Crystalline Films

Herein we report a group of five planar chiral molecules as photon-mode chiral switches for the reversible control of the self-assembled superstructures of doped chiral nematic liquid crystals. The chiral switches are composed of an asymmetrically substituted aromatic moiety and a photoisomerizing azobenzene unit connected in a cyclic manner through methylene spacers of varying lengths. All the molecules show conformational restriction in the rotation of the asymmetrically substituted aromatic moiety in both the E and Z states of the azobenzene units resulting in planar chirality with separable enantiomers. Our newly synthesized compounds in pure enantiomeric form show high helical twisting power (HTP) in addition to an improved change in HTP between the E and Z states. The molecule with a diphenylnaphthalene unit shows the highest ever known initial helical twisting power among chiral dopants with planar chirality. In addition to the reversible tuning of reflection colors, we employed the enantiomers of these five compounds in combination with four nematic liquid crystalline hosts to study their properties as molecular machines; the change in HTP of the chiral dopant upon photoisomerization induces rotation of the texture of the liquid crystal surfaces. Importantly, this study has revealed a linear dependence of the ratio of the difference between HTPs before and after irradiation against the absolute value of the initial HTP, not the absolute value of the change in helical twisting power between two states, on the angle of rotation of micro-objects on chiral nematic liquid crystalline films. This study has also revealed that a change in irradiation intensity does not affect the maximum angle of rotation, but it does affect the speed of rotational reorganization of the cholesteric helix.

Chemistry and applications of nanocrystalline cellulose and its derivatives: A nanotechnology perspective

AbstractNanocrystalline cellulose (NCC) is an emerging renewable nanomaterial that holds promise in many different applications, such as in personal care, chemicals, foods, pharmaceuticals, etc. By appropriate modification of NCC, various functional nanomaterials with outstanding properties, or significantly improved physical, chemical, biological, as well as electronic properties can be developed. The nanoparticles are stabilised in aqueous suspension by negative charges on the surface, which are produced during the acid hydrolysis process. NCC suspensions can form a chiral nematic ordered phase beyond a critical concentration, i.e. NCC suspensions transform from an isotropic to an anisotropic chiral nematic liquid crystalline phase. Due to its nanoscale dimension and intrinsic physicochemical properties, NCC is a promising renewable biomaterial that can be used as a reinforcing component in high performance nanocomposites. Many new nanocomposite materials with attractive properties were obtained by the physical incorporation of NCC into a natural or synthetic polymeric matrix. Simple chemical modification on NCC surface can improve its dispersability in different solvents and expand its utilisation in nano‐related applications, such as drug delivery, protein immobilisation, and inorganic reaction template. This review paper provides an overview on this emerging nanomaterial, focusing on the surface modification, properties and applications of NCC.

Properties of spatial solitons in chiral nematic liquid crystal cells

In this work we demonstrate the properties of spatial solitary waves in chiral nematic liquid crystalline film. Such self-trapped beams were created due to the optical reorientation nonlinearity for the light power of a few tenths of milliwats at the distances of a few millimeters. Additionally, it is shown that the direction of propagation of such nematicons can be modified by changing the light beam input polarization as well as by applying an external electric field. Full Text: PDF