Liquid Crystal Order Research Articles

Liquid Crystal Ordering on Conjugated Polymers Film Morphology for High Performance

ABSTRACTThe electronic performance of conjugated polymers depends on the microstructure of the polymer films. A percolated network morphology with high crystallinity, ordered intermolecular packing and long‐range order is beneficial for charge transport. In recent reports, some conjugated polymers have been shown to exhibit liquid crystallinity. The appearance of liquid crystalline ordering provides a new solution to solve the difficulties in microstructure manipulation. In this review, we summarize how liquid crystallinity can assist molecular arrangement and guide long‐range orientation during film processing, leading to high charge mobility. We expect that this article could draw more attention to the liquid crystallinity of conjugated polymers. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1572–1591

Monodisperse Liquid Crystal Network Particles Synthesized via Precipitation Polymerization.

The production of liquid crystalline (LC) polymer particles with a narrow size distribution on a large scale remains a challenge. Here, we report the preparation of monodisperse, cross-linked liquid crystalline particles via precipitation polymerization. This versatile and scalable method yields polymer particles with a smectic liquid crystal order. Although the LC monomers are randomly dissolved in solution, the oligomers self-align and LC order is induced. For the polymerization, a smectic LC monomer mixture consisting of cross-linkers and benzoic acid hydrogen-bonded dimers is used. The average diameter of the particles increases at higher polymerization temperatures and in better solvents, whereas the monomer and initiator concentration have only minor impact on the particle size. After deprotonating of the benzoic acid groups, the particles show rapid absorption of a common cationic dye, methylene blue. The methylene blue in the particles can be subsequently released with the addition of Ca2+, while monovalent ions fail to trigger the release. These results reveal that precipitation polymerization is an attractive method to prepare functional LC polymer particles of a narrow size distribution and on a large scale.

Design Parameters and Principles of Liquid-Crystal-Templated Synthesis of Polymeric Materials via Photolithography.

The design parameters and principles for the synthesis of polymeric microscopic objects using a method that combines photolithography and liquid crystal (LC) molecular templates have been demonstrated. Specifically, mixtures of a reactive mesogen (RM257) and nonreactive LC (E7) were polymerized using UV light and a photomask. We used photomasks with circular, triangular, rectangular, square, star-shaped, and heart-shaped features to provide initial shapes to the objects. Then, the unreacted parts were extracted and the polymeric objects were allowed to shrink anisotropically as defined by the ordering symmetry of the LC mixture. The initial configuration of the LC mixtures played a critical role in determining the final shapes of the polymeric objects formed after shrinking, which resulted in chiral twisting and bending, leading to more than 20 different shapes. We found that the pitch size of the bulk chiral twisted objects depends linearly on the angle of chiral twist of the LCs, whereas it was independent of their thickness and length ranging from 1.5 to 160 μm and 100 μm to 2.45 cm, respectively. The shapes of the polymeric objects synthesized from LC films with bent LC ordering, however, were critically dependent on the thickness of the objects due to the interplay between the elastic energy and surface anchoring of the LCs. The critical role of LC elasticity was observed for thicknesses below 20 μm, above which surface anchoring was dominant in determining the shapes. Overall, the proposed method was shown to provide a precise control over the three-dimensional architectures of the objects with size range that covers the micro and macro scales, which would find use in fields ranging from emulsion stabilization and catalysis to micromachines and artificial muscles.

Organic thin-film transistors with liquid crystalline polymer insulator integrated for solution-processed organic light-emitting devices

We develop a solution-processed organic thin-film transistor (S-OTFT) with high stability and uniformity using a liquid crystalline polymer (LCP) as a gate insulator. It is found that the liquid crystal order in the LCP is one of critical factors governing the electrical properties of the S-OTFT. The photo-polymerized LCP layer exhibits the chain ordering which significantly improves the dielectric characteristics of the insulator layer and the reliability of the S-OTFT. A prototype array of 3 × 3 solution-processed organic light-emitting diodes integrated with the S-OTFTs based on the LCP insulator shows the high uniformity of light emission during operation.

Lyotropic Liquid Crystals from Colloidal Suspensions of Graphene Oxide

Lyotropic liquid crystals from colloidal particles have been known for more than a century, but have attracted a revived interest over the last few years. This is due to the developments in nanoscience and nanotechnology, where the liquid crystal order can be exploited to orient and reorient the anisotropic colloids, thus enabling, increasing and switching the preferential properties of the nanoparticles. In particular, carbon-based colloids like carbon nanotubes and graphene/graphene–oxide have increasingly been studied with respect to their lyotropic liquid crystalline properties over the recent years. We critically review aspects of lyotropic graphene oxide liquid crystal with respect to properties and behavior which seem to be generally established, but also discuss those effects that are largely unfamiliar so far, or as of yet of controversial experimental or theoretical outcome.

Predicting molecular ordering in a binary liquid crystal using machine learning

ABSTRACTMachine learning is a category of AI technology that is utilized in the product development cycle in numerous industries. It was reported that machine learning can be applied to predict the chemical properties of functional materials, for example, the self-assembly of surfactant solutions (Nanoscale, 2018, 10, 16013) and the chemical reactions of copper nanoparticles (ACS Energy Lett., 2018, 3, 2983). A liquid crystal (LC) molecule is a representative functional material. Monodisperse systems have been targeted in many theoretical studies; however, the resulting products usually have a polydisperse distribution. It has been reported in several studies that the properties exhibited by polydisperse systems are different from those observed in monodisperse systems. In this study, we focus on the physical properties of polydisperse systems i.e. the ratio of binary LC molecules on the phase transition temperature and the possibility of predicting the physical properties of the system using machine learning. A relatively high prediction accuracy was obtained using machine learning. This study demonstrates that machine learning can be utilized to predict the phase transition temperature of polydispersed LC systems. The results of this study will contribute to the further development of material science and molecular design via the application of machine learning.

The Effect of Bulky Substituents on Two π-Conjugated Mesogenic Fluorophores. Their Organic Polymers and Zinc-Bridged Luminescent Networks.

From a dicyano-phenylenevinylene (PV) and an azobenzene (AB) skeleton, two new symmetrical salen dyes were obtained. Terminal bulky substituents able to reduce intermolecular interactions and flexible tails to guarantee solubility were added to the fluorogenic cores. Photochemical performances were investigated on the small molecules in solution, as neat crystals and as dopants in polymeric matrixes. High fluorescence quantum yield in the orange-red region was observed for the brightest emissive films (88% yield). The spectra of absorption and fluorescence were predicted by Density Functional Theory (DFT) calculations. The predicted energy levels of the frontier orbitals are in good agreement with voltammetry and molecular spectroscopy measures. Employing the two dyes as dopants of a nematic polymer led to remarkable orange or yellow luminescence, which dramatically decreases in on-off switch mode after liquid crystal (LC) order was lost. The fluorogenic cores were also embedded in organic polymers and self-assembly zinc coordination networks to transfer the emission properties to a macro-system. The final polymers emit from red to yellow both in solution and in the solid state and their photoluminescence (PL) performance are, in some cases, enhanced when compared to the fluorogenic cores.

Polyunsaturated Phospholipid Modified Membrane Degradation Catalyzed by a Secreted Phospholipase A2.

To optimize the compositions of the lipid-based nanomedicine and to advance understanding of the roles of polyunsaturated phospholipids in biological membranes, this study examined the effects of polyunsaturated phospholipids on the degradation of giant unilamellar vesicles catalyzed by a secreted phospholipase A2 (sPLA2) using fluorescence microscopy. Molecular interfacial packing, interaction, and degradation of the films containing various mixing ratios of saturated and polyunsaturated phospholipids were quantified using a Langmuir trough integrated with synchrotron X-ray surface scattering techniques. It was found that a high molar fraction (0.63 and above) of polyunsaturated phospholipids not only enhanced the rate of sPLA2-catalyzed vesicle degradation but also changed the vesicle deformation process and degradation product morphology. Hydrolysis of the saturated phospholipids generated highly ordered liquid crystal domains, which was reduced or prohibited by the presence of the polyunsaturated phospholipids in the reactant film.

Morphing of liquid crystal surfaces by emergent collectivity

Liquid crystal surfaces can undergo topographical morphing in response to external cues. These shape-shifting coatings promise a revolution in various applications, from haptic feedback in soft robotics or displays to self-cleaning solar panels. The changes in surface topography can be controlled by tailoring the molecular architecture and mechanics of the liquid crystal network. However, the nanoscopic mechanisms that drive morphological transitions remain unclear. Here, we introduce a frequency-resolved nanostrain imaging method to elucidate the emergent dynamics underlying field-induced shape-shifting. We show how surface morphing occurs in three distinct stages: (i) the molecular dipoles oscillate with the alternating field (10–100 ms), (ii) this leads to collective plasticization of the glassy network (~1 s), (iii) culminating in actuation of the topography (10–100 s). The first stage appears universal and governed by dielectric coupling. By contrast, yielding and deformation rely on a delicate balance between liquid crystal order, field properties and network viscoelasticity.

Exactly solvable Kondo lattice model in the anisotropic limit

In this paper we introduce an exactly solvable Kondo lattice model without any fine-tuning local gauge symmetry. This model describes itinerant electrons interplaying with a localized magnetic moment via only longitudinal Kondo exchange. Its solvability results from conservation of the localized moment at each site, and is valid for arbitrary lattice geometry and electron filling. A case study on square lattice shows that the ground state is a N\'{e}el antiferromagnetic insulator at half-filling. At finite temperature, paramagnetic phases including a Mott insulator and correlated metal are found. The former is a melting antiferromagnetic insulator with a strong short-range magnetic fluctuation, while the latter corresponds to a Fermi liquid-like metal. Monte Carlo simulation and theoretical analysis demonstrate that the transition from paramagnetic phases into the antiferromagnetic insulator is a continuous $2D$ Ising transition. Away from half-filling, patterns of spin stripes (inhomogeneous magnetic order) at weak coupling, and phase separation at strong coupling are predicted. With established Ising antiferromagnetism and spin stripe orders, our model may be relevant to a heavy fermion compound CeCo(In$_{1-x}$Hg$_{x}$)$_{5}$ and novel quantum liquid-crystal order in a hidden order compound URu$_{2}$Si$_{2}$.

Induced orientational molecular ordering in nematic liquid crystals with magnetic nanoparticles

Induced orientational molecular ordering in nematic liquid crystals with magnetic nanoparticles

Liquid-crystal organization of liver tissue.

Functional tissue architecture originates by self-assembly of distinct cell types, following tissue-specific rules of cell-cell interactions. In the liver, a structural model of the lobule was pioneered by Elias in 1949. This model, however, is in contrast with the apparent random 3D arrangement of hepatocytes. Since then, no significant progress has been made to derive the organizing principles of liver tissue. To solve this outstanding problem, we computationally reconstructed 3D tissue geometry from microscopy images of mouse liver tissue and analyzed it applying soft-condensed-matter-physics concepts. Surprisingly, analysis of the spatial organization of cell polarity revealed that hepatocytes are not randomly oriented but follow a long-range liquid-crystal order. This does not depend exclusively on hepatocytes receiving instructive signals by endothelial cells, since silencing Integrin-β1 disrupted both liquid-crystal order and organization of the sinusoidal network. Our results suggest that bi-directional communication between hepatocytes and sinusoids underlies the self-organization of liver tissue.

Liquid Crystal based Detection of Pb(II) Ions Using Spinach RNA as Recognition Probe.

We report a new method for label-free, sensitive, and facile detection of lead(II) ions (Pb2+) based on an aptamer-target binding event, which is recognized by orientations of liquid crystals (LCs) at aqueous interfaces. The LC film suspended in the aqueous phase demonstrated a homeotropic orientation in contact with a cationic surfactant cetyltrimethylammonium bromide (CTAB) due to self-assembly of CTAB molecules at the aqueous-LC interface. The ordering of LC subsequently changed to planar in the presence of the spinach RNA aptamer (SRNA) due to interactions between CTAB and SRNA. In the presence of the Pb2+ ion, the ordering of LC changed to homeotropic caused by reorganization of CTAB at the LC-aqueous interface. This is due to formation of more stable quadruplex structures of SRNA with Pb2+ ions in comparison to the CTAB-SRNA complex. The sensor exhibited a detection limit of 3 nM, which is well below the permissible limit of Pb2+ in drinking water. Our experiments establish that addition of Pb2+ leads to (i) the formation of Pb2+-SRNA complexes and (ii) a decrease in density of SRNA on the LC interface, but additional studies are required to determine which of these processes underlie the response of the LCs to the Pb2+. We have also demonstrated the potential application of the LC sensor for detection of Pb2+ in tap water. Unlike current laboratory-based heavy-metal-ion assays, this method is comparatively simple in terms of instrumentation, operation, and optical readout.

NMR of cellulose nanocrystals, mesoporous media, and liquid crystal assemblies

ABSTRACT This article gives an overview of cellulose nanocrystals (CNCs), liquid crystal templating based on suspensions of CNC rods, and their corresponding templated mesoporous materials. NMR cryoporometry was used to give pore size distributions in chiral nematic mesoporous silica (CNMS) and organosilica (CNMO) films, while NMR pulsed-field gradient technique was used to study diffusion anisotropy of water absorbed in these films. 14N-NMR was used to probe the orientation of a calamite liquid crystal (LC) confined in the pores of CNMO films. Effects due to confining hydrogen-bond assemblies (HBAs) in CNMS and CNMO films were investigated by means of 2H-NMR and 19F-NMR. These results were compared with the ordering in the corresponding neat HBA. The ability to tune/switch the film’s optical responses via orientation ordering of LCs in the pores of CNMO films was demonstrated by NMR.

Shining Light on Liquid Crystal Polymer Networks: Preparing, Reconfiguring, and Driving Soft Actuators

AbstractSoft actuators based on liquid crystal polymer networks (LCNs) have emerged as an exciting research topic due to many envisioned applications in areas such as soft robotics and self‐regulating devices. The infatuation stems from the amazing ability of LCNs to display reversible, large amplitude, and complex shape change as well as locomotion upon a stimuli‐triggered phase transition of mesogens between ordered liquid crystal and disordered isotropic state. Among the various stimuli, light arguably is the most attractive choice. Light can easily be adjusted for its wavelength, intensity, or polarization, structured by means of photomasks or interference patterns, and applied to a target remotely and with high spatiotemporal resolution. Indeed, much research effort is dedicated to LCN actuators that are designed to respond to light in many ways, with light being used not only as an external energy source to drive the shape changes or motion of LCN actuators, but also as a versatile tool in their fabrication and reconfiguration. In this Review, recent achievements are highlighted, a number of important issues are discussed, and critical analysis on the use of light in making, reconfiguring, and driving LCN actuators is provided.

Sustained multiferroicity in liquid crystal induced by core/shell quantum dots

Sustained multiferroicity along with the ferromagnetic ordering in a ferroelectric liquid crystal (FLC) on incorporation of Co-ZnO/ZnO core/shell (CZZ) quantum dots (QDs) is confirmed by ferroelectric (P-E) and ferromagnetic (M-H) hysteresis measurements. An appropriate amount of CZZ QDs was added into pure FLC (KCFLC 7S) material to study its ferroelectric and ferromagnetic properties. Increased cobalt concentration in the core of CZZ QDs enhances the magnitude of saturation magnetization. The inherent magnetic field of core/shell QDs is coupled with the director field of the FLC molecules without altering the intrinsic properties of host FLC and dopant QDs, which reveals sustained multiferroic behavior. Notably, the optimized concentration of QDs does not disturb the intrinsic ferroelectric nature of the host as confirmed by ferroelectric and helical pitch measurements. The outcome of this work would be beneficial for future QD based liquid crystal displays that exhibit both electric and magnetic memory within itself.

Liquid Crystal ordering of DNA Dickerson Dodecamer duplexes with different 5’- Phosphate terminations

The onset of liquid crystal (LC) phases in concentrated aqueous solutions of DNA oligomers crucially depends on the end-to-end interaction between the DNA duplexes, which can be provided by the aromatic stacking of the terminal base-pairs or by the pairing of complementary dangling-ends. Here we investigated the LC behavior of three blunt-end 12-base-long DNA duplexes synthesized with hydroxyl, phosphate and triphosphate 5’-termini. We experimentally characterized the concentration-temperature phase diagrams and we quantitatively estimated the end-to-end stacking free energy, by comparing the empirical data with the predictions of coarse-grained linear aggregation models.The preservation of LC ordering, even in presence of the bulky and highly charged triphosphate group, indicates that attractive stacking interactions are still present and capable of induce linear aggregation of the DNA duplexes. This finding strengthens the potential role of chromonic like self-assembly for the prebiotic formation of linear polymeric nucleic acids.

The short-range order in liquid and A15 crystal of zirconium

Molecular dynamic simulations have been carried out to investigate the crystallization mechanism during rapid cooling and isothermal relaxation for Zirconium (Zr) under a pressure of 100 GPa. The properties of the simulated system are analysed in terms of the system energy, the pair distribution function (PDF), and the largest standard cluster analysis. It is found that the so called topologically close-packed (TCP) local structures dominate in number in liquid, supercooled liquid and the final solid. Both solidification and relaxation crystallize into an A15 phase rather than the simple bcc or hcp crystals, the metastable and stable crystal of Zr under the ambient condition. Interestingly on PDF curves for liquids and super-liquids, left to the first major peak (at around r = 3.0 Å) there is a mini-peak (at around r = 1.87 Å) that decreases with the decrease of temperature and vanishes when crystallization ends. Further analysis reveals that the mini-peak originates from dynamical compact atomic pairs that are however almost nothing to do with TCP local structures. In addition, the multi characteristic lengths of the A15 unit (composed of Z12 and Z14 local structures with ratio of 1:3) result in the distinct split of the first and second peaks on the PDF curves.

Protein triggered ordering transitions in poly (L-lysine)-coated liquid crystal emulsion droplets

ABSTRACTHere, we report a simple and label-free methodology for real-time monitoring of adsorption of proteins such as bovine serum albumin (BSA), concanavalin A (ConA) (a lectin) and cathepsin D (CathD) (a tumour marker) on micrometer-sized poly (L-lysine) (PLL) functionalised liquid crystal (LC) droplets dispersed in aqueous phases. Earlier, we had demonstrated that PLL, a positively charged natural peptide, can induce homeotropic ordering of LCs at LC-aqueous interface, and thus PLL-adsorbed LC droplets showed radial director configuration. Herein, it was observed that subsequent non-specific adsorption of anionic proteins such as BSA, ConA and CathD can trigger a quick transition in director configuration of PLL-LC droplets (primarily dominated by electrostatic interactions) to pre-radial or bipolar, thus acting as a simple optical probe for detection of these proteins up to μg/mL of concentrations. Further, the detection limits for these proteins are found to vary (BSA<ConA<CathD) which follow the similar order as their anionic charges, thus suggesting the role of different binding affinities of protein-PLL in realising the director configuration of LC droplets. Overall, this study offers new pathways utilising ordering transition in LC droplets which will strengthen the principles to recognise biomolecular interactions for various interfacial and sensing applications.

Giant electrocaloric response in smectic liquid crystals with direct smectic-isotropic transition

Electrocaloric materials have become a viable technology for solid state heat management applications. We demonstrate both theoretically and experimentally that liquid crystals (LCs) can be exploited as efficient electrocaloric materials. Numerical and experimental investigations determine the conditions under which the strongest electrocaloric effect (ECE) responses are expected in LCs. Specifically, we show that a large ECE can be expected at the isotropic-nematic and in particular at the isotropic-smectic A phase transition. In our theoretical study, LC ordering is modelled using a Landau – de Gennes - Ginzburg mesoscopic approach. The simulation results are in qualitative agreement with our high precision electrocaloric measurements conducted on 8CB and 12CB liquid crystals. In the latter, we obtained ΔTEC ~ 6.5 K, corresponding to the largest response measured so far in LCs. The fluid property of LC electrocaloric heat cooling elements could lead to the development of devices with a higher coefficient of performance and thus better cooling power yield per mass of the ECE-based device.