Self-assembled Liquid Crystals Research Articles

Self-Assembling Anti-Freezing Lamellar Nanostructures in Subzero Temperatures.

The requirement for cryogenic supramolecular self-assembly of amphiphiles in subzero environments is a challenging topic. Here, the self-assembly of lamellar lyotropic liquid crystals (LLCs) are presented to a subzero temperature of -70 °C. These lamellar nanostructures are assembled from specifically tailored ultra-long-chain surfactant stearyl diethanolamine (SDA) in water/glycerol binary solvent. As the temperature falls below zero, LLCs with a liquid-crystalline Lα phase, a tilted Lβ phase, and a new folded configuration are obtained consecutively. A comprehensive experimental and computational study is performed to uncover the precise microstructure and formation mechanism. Both the ultra-long alkyl chain and head group of SDA play a crucial role in the formation of lamellar nanostructures. SDA head group is prone to forming hydrogen bonds with water, rather than glycerol. Glycerol cannot penetrate the lipid layer, which mixes with water arranging outside of the lipid bilayer, providing an ideal anti-freezing environment for SDA self-assembly. Based on these nanostructures and the ultra-low freezing point of the system, a series of novel cryogenic materials are created with potential applications in extremely cold environments. These findings would contribute to enriching the theory and research methodology of supramolecular self-assembly in extreme conditions and to developing novel anti-freezing materials.

Terminal Group Effect on Two-Dimensional Self-Assembly of Fluorenone-Based Liquid Crystals at the Solid/Liquid Interface.

Self-assemblies of two fluorenone-based derivatives (FE and FEC) consisting of a central 2,7-diphenyl-9-fluorenone polar moiety but differing in the flexible terminal groups were investigated by scanning tunneling microscopy (STM) at the 1-octanoic acid/HOPG interface under different concentrations and density functional theory calculation (DFT). STM results reveal a concentration-dependent polymorphic self-assembly behavior for FE, but without the presence of co-adsorbed solvents. As the concentration decreases, the dimer, bracket-like, and ribbon-like self-assembled structures were observed. On the contrary, FEC molecules assemble into only a type of oval-shaped morphology by the intermolecular N···H-O hydrogen bonds with the solvent molecules. Combined with DFT calculations, it can be deduced that the intermolecular van der Waals forces, dipole-dipole interactions, and hydrogen bonding are the main driving forces to stabilize the molecular packing of fluorenone-based polycatenars with strong polarity. Our work is of significance at the molecular level to further clarify the intermolecular interactions and conformational effects on the formation of molecular packing structures with liquid crystal property.

Exploring the interplay of liquid crystal orientation and spherical elastic shell deformation in spatial confinement.

The application of liquid crystal technology typically relies on the precise control of molecular orientation at a surface or interface. This control can be achieved through a combination of morphological and chemical methods. Consequently, variations in constrained boundary flexibility can result in a diverse range of phase behaviors. In this study, we delve into the self-assembly of liquid crystals within elastic spatial confinement by using the Gay-Berne model with the aid of molecular dynamics simulations. Our findings reveal that a spherical elastic shell promotes a more regular and orderly alignment of liquid crystals compared to a hard shell. Moreover, during the cooling process, the hard-shell confined system undergoes an isotropic-smectic phase transition. In contrast, the phase behavior within the spherical elastic shell closely mirrors the isotropic-nematic-smectic phase transition observed in bulk systems. This indicates that the orientational arrangement of liquid crystals and the deformations induced by a flexible interface engage in a competitive interplay during the self-assembly process. Importantly, we found that phase behavior could be manipulated by altering the flexibility of the confined boundaries. This insight offers a fresh perspective for the design of innovative materials, particularly in the realm of liquid crystal/polymer composites.

Surface proton hopping conduction mechanism dominant polymer electrolytes created by self-assembly of bicontinuous cubic liquid crystals.

For the development of the next generation of fuel cells, it is essential to create an innovative design principle of polymer electrolytes that is beyond extension of the existing strategy. In the present study, we focused on the surface hopping proton conduction mechanism where an activation energy for proton conduction is greatly reduced by decreasing the distance between SO3- groups. Our gyroid nanostructured polymer film (Film-G), with a hydrophilic surface where the SO3- groups are aligned densely and precisely, shows high proton conductivity of the order of 10-2 S cm-1 when the water content is about 15 wt%. We reveal that the high proton conductivity of Film-G is attributed to the exhibition of an extremely-fast surface hopping conduction mechanism due to the reduced activation energy barrier along the gyroid minimal surface. This finding should introduce a game-changing novel opportunity in polymer electrolyte design.

The effect of the number of cyanostilbene building blocks on the self-assembly and photophysical property of pyrene-based liquid crystals

The synthesis, self-assembly and physical properties of two series of di/tetra-substituted pyrene-based liquid crystals were reported. These compounds were synthesized by using Suzuki coupling and Knoevenagel reactions as key steps. The effects of the number of cyanostilbene arms connecting to central pyrene on the mesomorphic and emission behaviors with structurally related compounds were investigated. The lower pyrene-based homologue containing two cyanostilbene arms could self-assemble into rectangular columnar phase in which two molecules aggregated into a disc, whereas the higher pyrene-based homologues could self-assemble into hexagonal columnar phase in which four molecules aggregated into a disc. The pyrene-based liquid crystals containing four cyanostilbene arms could also self-assemble into hexagonal columnar phase in which two molecules aggregated into a disc. The self-assembly process and the models for arrangements within these columnar phases were proposed and discussed in detail. These compounds also exhibited distinct slovatochromism and strong fluorescence in both solution and aggregated states. Therefore, controlling molecular structures of functional liquid crystal materials was an efficient way to tune the self-assemblies and emission properties.

Liquid Crystal Emulsions: A Versatile Platform for Photonics, Sensing, and Active Matter.

The self-assembly of liquid crystals (LCs) is a fascinating method for controlling the organization of discrete molecules into nanostructured functional materials. Although LCs are traditionally processed in thin film, their confinement within micrometre-sized droplets has recently revealed new properties and functions for the design of next-generation soft responsive materials. These recent findings have enabled a wealth of unprecedented applications in photonics (e.g., reflectors, lasing materials), sensing (e.g., detection of biomolecules, pathogens), soft robotics (e.g., micropumps, artificial muscles), and beyond. This minireview focuses on recent developments in the design of LC emulsions and highlights a variety of novel potential applications. We also offer perspectives on the opportunities and new directions towards the implementation of LC emulsions in future innovative technologies.

Impact of terminal group on azobenzene liquid crystal dimers for photo-responsive optical storage devices

Three new series of photo responsive dimers bearing different terminal functional groups (-CN, -COOEt, -OMe) and variable aliphatic spacers have been synthesized and investigated in detail. The molecular structures of the new materials were proved using different spectroscopic techniques and their liquid crystal self-assembly was characterized using differential scanning calorimetry (DSC), polarized light microscope (POM) and X-ray diffraction (XRD). Moreover, their photo switching behaviour was investigated in details in solution. The results revealed that, almost all members of the dimeric materials are mesomorphic exhibit either nematic or both smectic A and nematic phases. Under UV illumination the materials show interesting photo-switching properties, reaching a photo-stationary state in 40 s and a thermal back-relaxation time of approximately 35 h in solution. Finally, a fabricated device authenticates the potential of the reported materials for optical storage devices.

Darifenacin Self-assembled Liquid Crystal Cubic Nanoparticles: a Sustained Release Approach for an Overnight Control of Overactive Bladder

The current study is regarding the development and characterization of Darifenacin-loaded self-assembled liquid crystal cubic nanoparticles (LCCN). An anhydrous approach was used for the preparation of these cubic nanoparticles using a hydrotropic agent (propylene glycol), with minimal energy input. Upon dispersion in aqueous medium, the system was successfully transformed to cubosomal nanoparticles counterpart as depicted by transmission electron micrographs. A Box-Behnken design was used to optimize formulation variables, namely A: amount of GMO, B: amount of Pluronic F127, C: amount of PG, and D: amount of HPMC. The design has generated 29 formulae which were tested regarding drug content uniformity, dispersibility in water, particle size, zeta potential, polydispersity index, and in vitro release behavior. The numerical optimization algorithms have generated an optimized formula with high desirability ≈ 1. The optimized formula displayed small particle size, good homogeneity, and zeta potential along with controlled in vitro release profile and ex vivo permeation through rabbit intestine. Thus, self-assembled LCCN might offer an alternative anhydrous approach for the preparation of cubosomal nanoparticles with controlled release profile for a possibly better control of overactive bladder syndrome which tremendously affect the overall life quality.Graphical

Substituents role in highly symmetrical 1,2,3-triazoles derivatives toward self-assembly of soft liquid crystals

Triazole bent-core mesogens based on symmetrical bent-shaped of two 1,2,3-triazole ring arms were synthesized and characterized. The the thermail stability of those new synthesised mesogens from the embient temperature to 215 °C giving mesogenic phase transitions over a wide temperature range is investigated. A study of different substituents located on the rigid bentcore was carried out for compact supramolecular innovated architectures which were produced by self-assembly of many triazoles soft crystals with a liquid crystals behaviour. The synthetic procedures, characterizations and polymorphism of four novel bent-core mesogens comprising symmetrical 1,2,3-triazole arms were demonstrated. The preparation process was carried out through‘‘click chemistry’’ via Cu-catalyzed azide-alkyne cycloaddition of nitro- and alkyl-substituted aromatic azides with aromatic compounds, comprising terminal alkyne groups and long alkyl or alkoxy side-chains. The triazole derivatives were fully characterized by 1H/13C NMR, Fourier-transform infrared spectroscopy (FTIR) and elemental analysis. The mesophases and textures were examined by employing polarizing optical microscope (POM), differential scanning calorimetry (DSC) and X-ray Diffraction (XRD). The analogues with shorter alkoxy terminal substituents displayed higher mesomorphic properties with wide mesomorphic temperature ranges compared to analogues with shorter alkoxy terminals. The morphological characteristics of the self-assembled triazoles were investigated by scanning electron microscopy (SEM) which demonstrated arrangement of highly ordered columnar architectures. These orders were driven by layer to next layer adjacent influences and π-π stacking. The effect of 1,2,3-triazole ring and length of terminal aliphatic chains on the liquid crystalline performance were discussed. Through an appropriate choice of lateral structures employing “click chemistry’’, both transition temperature and mesophases ranging from isotropic to columnar or B1/B4-like supramolecular liquid crystalline aggregates can be tuned.

A Novel Molecular Reservoir Based on Reverse Self-Assembled Liquid Crystals - A New Strategy for Prolonging the Duration in Action of Analgesics

PurposeThe aim of this study was to develop liquid crystal (LC) precursors to obtain novel long-acting analgesics for injection based on depot systems and compare the difference between the cubic and hexagonal precursors in delivering Diclofenac sodium (DS). MethodsDiclofenac sodium liquid crystal precursor injections were prepared and characterized, followed by in vitro release, pharmacodynamic, and pharmacokinetic studies. ResultsThe optimal formulations were prepared with a ratio of Phytantriol/ethanol/water as 76:19:5 for cubic LC precursors, and a ratio of Phytantriol/ethanol/water/Vitamine-E acetate as 72:18:5:5 for hexagonal, both loading various drug dosages (2.5%, 3.75% and 5%), respectively. Polarized light microscopy and small angle diffraction confirmed that the precursors were isotropic fluids and transformed into gels with Pn3m or HII framework in water. Rheological studies have shown that precursors belong to Newtonian fluids and gels to pseudoplastic fluids. The release showed that the DS in the commercial injection (DS-inj) was completely liberated within 6 h, whereas only 46.55% and 49.73% of the DS in 2.5% cubic precursors and 2.5% hexagonal precursors were freed, respectively. Pharmacodynamic studies have shown that cubic, hexagonal and DS-inj raised the pain threshold in mice by 169.4%, 157.3% and 113.79%, respectively. The mean retention times of DS in cubic and hexagonal were 3.16 and 2.67 times longer than DS-inj, respectively, according to pharmacokinetic results. ConclusionIn conclusion, cubic and hexagonal are both promising analgesic sustained release formulations. In addition, based only on the current comparison, cubic seems to have a better long-acting effect.

Observation of helical self-assembly in cyclic triphosphazene-based columnar liquid crystals bearing chiral mesogenic units

Cyclotriphosphazene-based discotic liquid crystals are reported exhibiting helicoildal columnar arrangement and fluorescence turn-on phenomenon.

Mesogen-jacketed liquid crystal like block copolymers: synthesis and self-assembly to prepare 1D PC thin films

One dimensional photonic crystals (1D PCs) show great potential application in light control, sensors and functional displays. Self-assembly of block copolymer is a facile method to prepare 1D PCs in large area and easy processing. However, due to the low refractive index of polymer and the chain entanglement at very high molecular weight, it is difficult to prepare 1D PCs by self-assembly of linear block copolymers. In this work, mesogen-jacketed liquid crystals like block copolymers with two different lumbar connected benzene terephthalate derivatives and polynorbornene backbone are designed and synthesized. The big steric hindrance of the mesogenic benzene terephthalate derivatives extends the polymer backbone to be rigid, and the resultant block copolymers are rapidly self-assembled into lamellar structures with big domain spacing. The refractive indexes of the two blocks is differentiated by selecting the phenyl and decyl substitute group of benzene terephthalate derivatives. Hence, 1D PCs are prepared by self-assembly of mesogen-jacketed liquid crystals like block copolymers. The maximum reflectance is ranged from ultraviolet to near infrared by increasing the polymerization degree of the block copolymers from 400 to 1400 gradually. The lamellar structures are characterized by cross section scanning electron microscope and small angle X ray scattering. Mesogen-jacketed liquid crystal like block copolymer is favored in 1D PC preparation for its facile synthesis and flexible structure design.

Fibrous self-assembly of liquid crystal made by self-organisation

ABSTRACT Fibre structures of liquid crystals are of particular interest because they are expected to be used in optical fibres, optical devices, and lasers. Micrometre- sized liquid crystal self-assembly demonstrates new optical functions or interfacial interactions which cannot be observed in the bulk. Thermotropic liquid crystals organize fibres by phase transitions or shape changes. The fibrous self- assembly of liquid crystal made by self-organisation was reviewed in the study. We will also introduce the characteristics of these fibres as well as those of lyotropic myelin and lyotropic fibres. Theoretical research on the growth mechanism and physical properties of the fibres has also been summarized.

Synthesis, self-assembly and photophysical properties of AIEE-active triphenylamine-based discotic liquid crystals

Synthesis, self-assembly and photophysical properties of AIEE-active triphenylamine-based discotic liquid crystals

Tunable organic solvent nanofiltration in self-assembled membranes at the sub-1 nm scale.

Organic solvent–stable membranes exhibiting strong selectivity and high permeance have the potential to transform energy utilization in chemical separation processes. A key goal is developing materials with uniform, well-defined pores at the 1-nm scale, with sizes that can be tuned in small increments with high fidelity. Here, we demonstrate a class of organic solvent–stable nanoporous membranes derived from self-assembled liquid crystal mesophases that display such characteristics and elucidate their transport properties. The transport-regulating dimensions are defined by the mesophase geometry and can be controlled in increments of ~0.1 nm by modifying the chemical structure of the mesogen or the composition of the mesophase. The highly ordered nanostructure affords previously unidentified opportunities for the systematic design of organic solvent nanofiltration membranes with tailored selectivity and permeability and for understanding and modeling rejection in nanoscale flows. Hence, these membranes represent progress toward the goal of enabling precise organic solvent nanofiltration.

Optimizing the performance of the near-infrared (NIR) photothermal conversion via modulating the domain size of the chiral nematic phase in co-assembled cellulose nanocrystal composite films

The self-assembled liquid crystal nanostructure of CNCs provides an effective phase-segregation for PEDOT, thus improving the NIR photothermal performance of CNCs/PEDOT:PSS/OS/TA composites significantly.

Synthesis, Self-Assembly and Photoresponsive Behavior of Liquid Crystals Based on Azobenzene

A new amphiphilic surfactant (C4-Azo-C5-HDA) was formed by liquid crystals (LCs) based on azobenzene, whose structures were characterized by 1H-NMR spectroscopy. The reversible hydrogelation upon changes in temperature and light exposure was also studied. Under the irradiation of UV light, the trans-isomer of C4-Azo-C5-HDA rapidly photoisomerized to the cis-isomer, resulting in rapid disruption of the gel. The thermotropic liquid crystal behavior of the gelator was investigated via Differential Scanning Calorimetry (DSC) and Polarizing Optical Microscopy (POM). The biocompatibility experiment of multi-stimulus response of the liquid crystal provides a potential driving force for the development of biomaterials.

Ethanediamine induced self-assembly of long-range ordered GO/MXene composite aerogel and its piezoresistive sensing performances

Three-dimensional (3D) graphene oxide/MXene (GO/MX) composite aerogels with characters of lightweight, porous structure, and superior elasticity have attracted great attention in electromagnetic shielding, oil–water separation, and chemical catalysis, especially smart electronic sensors. However, due to the lack of adequate interaction force between GO and MX nanosheets, it is challenging to construct a high strengthand long-range ordered GO/MX aerogel, resultingin inferior mechanical properties and poor conductivity. Here, a facile gelation strategy is developed to form long-range ordered GO/MX aerogel by ethylenediamine (EDA) induced self-assembly of MX and GO liquid crystals (LCs). In this system, EDA plays dual roles of inducing ordered self-assembly of GO LCs nanosheets and strengtheninginteraction between GO and MX nanosheets. As a result, the obtained GO/MX aerogel with long-range ordered microstructure presents an outstanding mechanical elasticity of 9.5 kPa and a high conductivity of 0.99 S m−1. Especially, the assembled GO/MX-based sensor has an extremely low detection limit of ~ 0.2% strain, prominent physiological signal capture capability, and excellent durability over 10,000 compression/release cycles. This work paves the way for the potential applications of GO/MX composite aerogel in real-time human motion monitor, artificial skins, and flexible smart devices.

Insight Into the Superlubricity and Self-Assembly of Liquid Crystals.

Liquid crystals are promising molecular materials in the application of lubrication. Herein, the microscale solid superlubricity is accomplished by the construction of uniform and ordered self-assembly of several liquid crystals. The self-assembly structures on a highly oriented pyrolytic graphite (HOPG) surface are explicitly revealed by using scanning tunneling microscopy (STM). Meanwhile, the nanotribological performance of the self-assemblies are measured by using atomic force microscopy (AFM), revealing ultralow friction coefficients lower than 0.01. The interaction energies are calculated by density functional theory (DFT) method, indicating the positive correlation between friction coefficients and interaction strength. The effort on the self-assembly and superlubricity of liquid crystals could enhance the understanding of the nanotribological mechanism and benefit the further application of liquid crystals as lubricants.

Optical vector field rotation and switching with near-unity transmission by fully developed chiral photonic crystals

State-of-the-art nanostructured chiral photonic crystals (CPCs), metamaterials, and metasurfaces have shown giant optical rotatory power but are generally passive and beset with large optical losses and with inadequate performance due to limited size/interaction length and narrow operation bandwidth. In this work, we demonstrate by detailed theoretical modeling and experiments that a fully developed CPC, one for which the number of unit cells N is high enough that it acquires the full potentials of an ideal (N → ∞) crystal, will overcome the aforementioned limitations, leading to a new generation of versatile high-performance polarization manipulation optics. Such high-N CPCs are realized by field-assisted self-assembly of cholesteric liquid crystals to unprecedented thicknesses not possible with any other means. Characterization studies show that high-N CPCs exhibit broad transmission maxima accompanied by giant rotatory power, thereby enabling large (>π) polarization rotation with near-unity transmission over a large operation bandwidth. Polarization rotation is demonstrated to be independent of input polarization orientation and applies equally well on continuous-wave or ultrafast (picosecond to femtosecond) pulsed lasers of simple or complex (radial, azimuthal) vector fields. Liquid crystal-based CPCs also allow very wide tuning of the operation spectral range and dynamic polarization switching and control possibilities by virtue of several stimuli-induced index or birefringence changing mechanisms.