Liquid Crystal Composite Films Research Articles

Effect of Polymer Network Morphology on the Performance of Polymer Dispersed Liquid Crystal (PDLC) Composite Films

Effect of Polymer Network Morphology on the Performance of Polymer Dispersed Liquid Crystal (PDLC) Composite Films

Steric group-based polymer dispersed liquid crystal composite films with high contrast ratio, low driving voltage and small hysteresis

The unique phase-separated microstructure has endowed polymer dispersed liquid crystals (PDLCs) with outstanding electro-optical performances. However, their applications are hampered by the high driving voltage and low contrast ratio. Attempts to optimize the materials have been made in order to reduce the driving voltage without sacrificing the contrast ratio and other features. Herein, acrylate monomers with different steric end groups were introduced to fabricate PDLCs and their effects on the electro-optical properties and microstructure were investigated. Bipolar droplet configuration was observed in all samples implying tangential anchoring conditions. It was found that the steric end group could affect the morphology of polymer matrix and the electro-optical properties. By carefully adjusting the steric group and doping concentration, the contrast ratio could be enhanced and the driving voltage could be reduced. Besides, hysteresis could also be decreased. The research offers more choices for the construction of PDLCs from material perspective, promoting their potential applications.

SEM observation of light control liquid crystal composite films

SEM observation of light control liquid crystal composite films

Effects of oxygen heterocyclic acrylate monomers on the morphologies and electro-optical properties of polymer dispersed liquid crystal composite films

The current work aimed to fabricate polymer dispersed liquid crystal (PDLC) films using heterocyclic acrylate monomers containing oxygen atoms. The incorporation of oxygen heterocycles into the host polymer matrix significantly improved the electro-optical properties of PDLC films. Particularly, the high contrast ratio 330.0 was realized for the monomer Trimethylolpropane formal acrylate (TFA). Further, the excellent electro-optical properties, including low driving voltage (10.0 V), moderately high contrast ratio (64.0) and short response time (<8.0 ms) were obtained when the liquid crystals/polymer composite film thickness decreased from 20 μm to 8 μm. This work has provided a novel materials system to promote the application of PDLC films in the thin-layer liquid crystal display.

Micro-patterned photoalignment of CsPbBr3 nanowires with liquid crystal molecule composite film for polarized emission.

Photoalignment technology provides high potential for the manipulation of molecular orientations and has been widely used in liquid crystal displays. In this work, we align a luminescent film composite of CsPbBr3 nanowires (NWs) and liquid crystal molecules through photoalignment conducted on a PDMS template. We successfully define different orientations of CsPbBr3 NWs on the same substrate and the fluorescence micrographs clearly exhibit the orthogonal polarization direction of the two regions. On the basis of this research, we develop micro-photoalignment technology, which is promising for fabricating complex and precise nanostructures for photonic applications.

Effects of the methacrylate monomers with different end groups on the morphologies, electro-optical and mechanical properties of polymer dispersed liquid crystals composite films

ABSTRACT In this work, the effects of the methacrylate monomers with various end groups (methyl, hydroxyl, epoxy, tetrahydrofuran, cyclohexane, benzene and siloxane) on the morphologies, electro-optical and mechanical properties of polymer dispersed liquid crystal (PDLC) composite films were systematically investigated. The polymer network morphologies of the samples prepared with the monomers butyl methacrylate, tetrahydrofurfuryl methacrylate, cyclohexyl methacrylate or benzyl methacrylate were observed, and interestingly the polymer balls and polymer ball-networks morphologies were formed by introducing the hydroxypropyl methacrylate and glycidyl methacrylate, respectively. Meanwhile, the films obtained the optimal electro-optical properties with low driving voltage (10.7 V), fast response time (5.0 ms). Finally, the largest shearing force of the prepared PDLC composite films was two to three times better than that of the pristine sample with 3-(trimethoxysilyl)propyl methacrylate (TPMA) monomer doping or surface treatment methods. Thus, this work offers a new way to optimise the overall performance of PDLC films for practical applications.

P‐149: Enhanced Electro‐Optic Performances of the Optically Isotropic Liquid Crystal Displays Utilizing PEDOT: PSS

Optically isotropic liquid crystal (OILC) composite film in which nano‐sized LC droplets are embedded in a polymer matrix is highly useful for bendable displays and wearable photonics but a high operating voltage due to field shielding effect of the insulting matrix and low Kerr constant needs to be overcome. To address this challenge, a small amount of conductive materials PEDOT: PSS is doped into the OILCs. The LC cells with 2 and 3.5 wt% PEDOT: PSS doped OILCs exhibit improved driving voltages by 6.5% and 11.7% and on‐state transmittance by 10.3% and 30.1%, respectively, compared to conventional one. In addition, faster switching response times are achieved while the dark level remains to be unaltered.

A study on the mechanical and morphological behavior of polyurethane-encapsulated cholesteric liquid crystal composite films

This study explores the preparation and mechanical behavior of free-standing polymer-dispersed liquid crystal (PDLC) film membranes. Polyurethane (PU) was used as a thermoplastic polymer matrix to form these free-standing film membranes. Cholesteryl oleyl carbonate (COC) and cholesteryl pelargonate were used as liquid crystals (LCs) with different molecular weights. PDLC membranes were produced by casting method after LCs and polymer were mixed in the tetrahydrofuran solvent at room temperature. These membranes were formed at different concentration ratios of polymer and LCs. The relationship among the phase separation, LCs and polymer contents as well as the LCs molecular weights was investigated. The morphological structures of these membranes were studied using scanning electron microscopy (SEM). SEM images exhibited that the shapes of LC droplets embedded in PU matrix were more uniform and smaller than those of the membranes which include LC with lower molecular weight. The mechanical properties of the PDLC membranes were determined by carrying out the tensile tests. It was found that the membranes which include COC LC were more flexible.

Finger-Temperature-Detecting Liquid Crystal Composite Film for Anti-Counterfeiting Labels.

The development of the economy has increased the demand for anti-counterfeiting technologies, and with the traditional ones becoming known to the public, new and more effective ones are needed. In this study, a series of liquid crystal mixtures containing side-chain liquid crystal polymers and small-molecular-weight liquid crystals (LCs) were designed and prepared. The phase transition behavior and self-assembling structures of the LC mixtures were investigated by a combination of differential scanning calorimetry, polarized optical microscopy, and small-angle X-ray diffraction. The optical properties of the mixture film were characterized with a UV/VIS/IR spectrum study. The results reveal that the obtained film exhibited different optical modes between transparent, scattering, and selective reflection under finger-temperature control. Therefore, by the introduction of a coexisting thermal- or optical-polymer-dispersed network, a liquid crystal composite film with an integration of apparent optical switching modes and enhanced strength and toughness was successfully demonstrated. This research provides a versatile strategy for the design and preparation of liquid crystal anti-counterfeiting materials for practical use. In this study, a prototype finger-temperature-detecting anti-counterfeiting label was prepared, and its temperature-response property was demonstrated.

Smart Photovoltaic Windows: High‐Efficiency and Reliable Smart Photovoltaic Windows Enabled by Multiresponsive Liquid Crystal Composite Films and Semi‐Transparent Perovskite Solar Cells (Adv. Energy Mater. 33/2019)

Smart Photovoltaic Windows: High‐Efficiency and Reliable Smart Photovoltaic Windows Enabled by Multiresponsive Liquid Crystal Composite Films and Semi‐Transparent Perovskite Solar Cells (Adv. Energy Mater. 33/2019)

High‐Efficiency and Reliable Smart Photovoltaic Windows Enabled by Multiresponsive Liquid Crystal Composite Films and Semi‐Transparent Perovskite Solar Cells

AbstractSmart photovoltaic windows (SPWs) are functional devices possessing the capabilities of electrical power output, energy saving, and privacy protection by managing sunlight under external stimuli and potentially applicable in the fields of energy‐saving buildings, automobiles, and switchable optoelectronics. However, long response time, low power conversion efficiency (PCE), poor stability and cycling performance, and monostimuli responsive behavior restrict their practical applications. To address these issues, high‐efficiency and reliable SPWs are demonstrated by coupling multiresponsive liquid crystal/polymer composite (LCPC) films and semi‐transparent perovskite solar cells (ST‐PSCs). In this design, fast and multiple stimuli‐responsive LCPC films are utilized as an inside layer to control the transparency of SPWs. The ST‐PSCs with competitive PCE and qualified transparency acting as an outside layer offer energy generation functionality. Benefiting from repeatable transparency transition modulated by external stimuli, a series of working modes are achieved in the SPWs providing distinguished and stable energy generation, energy saving, and privacy protection performances.

A switchable optical diffuser based on a polymer/nematic liquid crystal composite film with transient polymer balls-networks microstructure

ABSTRACTWith the increasing development of multifunction liquid crystal displays (LCDs), multifunction optical diffusers have attracted more attention. In this work, switchable optical diffusers based on the transient polymer balls-networks in polymer/nematic liquid crystal composite films have been prepared and investigated, and the effects of thiol content, curing time, LC content and photo-initiator content on the polymer microstructures and optical properties of optical diffusers are systematically studied. An optical diffuser with the transient polymer balls-networks microstructure has achieved the high transmission (96.42%), high haze (90.49%), excellent optical diffusing ability and wide viewing angle of 150° (from −75° to 75°) on its off state. By the application of electric field of 40.0 voltage, the viewing angle of the optical diffuser turns to be narrower (from −60° to 60°), which gives great applications in tunable viewing angle devices and other electric optical devices.

Thiol-ene reaction based polymer dispersed liquid crystal composite films with low driving voltage and high contrast ratio

ABSTRACT In this study, polymer dispersed liquid crystal composite films are obtained via a one-step fabrication technique based on photo-initiated polymerization-induced phase separation in a thiol-vinyl ether reaction. The effects of the compositions of two vinyl monomers, curing light intensity, curing light time, liquid crystal content and thiol content on the electro-optic properties of the polymer dispersed liquid crystal films were systematically investigated. It was demonstrated that a composite film with a low driving voltage (33.7 V), high contrast ratio (228.1) and short response time (<5.0 ms) was achieved. This is of great significance for the potential applications of polymer dispersed liquid crystal composite films.

Investigation of thermodynamic properties of 4-decyloxybiphenyl-4′-carboxylic acid liquid crystal and preparation of polymer dispersed liquid crystal composite

In this study, firstly, retention behavior of solvents on the liquid crystalline material 4-decyloxybiphenyl-4′-carboxylic acid (DBCA) has been studied by inverse gas chromatography (IGC) technique. Liquid crystal (LC) selectivity was investigated using the acetate isomers by the IGC method at temperatures between 333.2 K and 543.2 K. Later on, the interactions of LC with n-octane, n-nonane, n-decane, undecane, dodecane, tridecane, n-propyl benzene, isopropyl benzene, ethylbenzene, chlorobenzene and toluene between 518.2 K and 543.2 K were examined. LC-solvent interaction parameters for Flory-Huggins theory, χ12∞, and equation of state theory, χ12∗, effective exchange energy parameters, Xeff, the weight fraction activity coefficent, Ω1∞, the partial molar heat of mixing at infinite dilution of the solvent, ∆H1∞, molar heat of vaporization of solvent, ∆HV and the partial molar heat of sorption of the solvent, ∆H1, s were obtained.Secondly, polymer dispersed liquid crystal (PDLC) composite film in composition 20/80 poly(methyl methacrylate) (PMMA):DBCA by weight was synthesized by solvent-induced phase separation method. The mesomorphic behavior of DBCA and PDLC composite has been investigated by differential scanning calorimetry (DSC) and optical polarizing microscopy (PM).

A novel optical diffuser based on polymer micro-balls-filled nematic liquid crystal composite film.

In this study, optical diffusers based on epoxy resin/thiol/nematic liquid crystal composites were prepared using different curing temperatures, curing times and curing agents (thiols). Additionally, the effects of the curing temperatures, the curing times and the thiols on the polymer ball microstructures and the optical properties of optical diffusers were investigated systematically. For applications of optical diffusers, the optimized curing temperature has been achieved by combining the high transmittance and high haze. A novel optical diffuser with ultrahigh transmittance (>94.0%), ultrahigh haze (>94.0%) and excellent diffusing ability has been obtained, of which the polymer morphology is single polymer micro-balls without aggregation.

Optical sensor platform based on cellulose nanocrystals (CNC) – 4′-(hexyloxy)-4-biphenylcarbonitrile (HOBC) bi-phase nematic liquid crystal composite films

The preparation of composite materials has gained tremendous attention due to the potential synergy of the combined materials. Here we fabricate novel thermal/electrical responsive photonic composite films combining cellulose nanocrystals (CNC) with a low molecular weight nematic liquid crystal (NLC), 4′-(hexyloxy)-4-biphenylcarbonitrile (HOBC). The obtained composite material combines both intense structural coloration of photonic cellulose and thermal and conductive properties of NLC. Scanning electron microscopy (SEM) results confirmed that liquid crystals coated CNC films maintain chiral nematic structure characteristic of CNC film and simultaneously, transversal cross-section scanning electron microscopy images indicated penetration of liquid crystals through the CNC layers. Investigated composite film maintain NLC optical properties being switchable as a function of temperature during heating/cooling cycles. The relationship between the morphology and thermoresponsive in the micro/nanostructured materials was investigated by using transmission optical microscopy (TOM). Conductive response of the composite films was proved by Electrostatic force microscopy (EFM) measurement. Designed thermo- and electro-responsive materials open novel simple pathway of fabrication of CNC-based materials with tunable properties.

An optical image stabilisation using a droplet manipulation on a liquid crystal and polymer composite film

ABSTRACTWe demonstrate an image system with an optical image stabilisation using a droplet manipulation on a liquid crystal (LC) and polymer composite film (LCPCF) to reduce motion blur while preserve image quality. Such an image system adopts a liquid lens on an LCPCF and the mechanism is on a basis of droplet movement on LCPCF whose position changes because electrically tunable orientations of LC molecules on the surface of LCPCF. The change of position of the liquid lens compensates the deviation of light as the image system is under a handshake vibration. As a result, the image system under handshake vibrations could keep a clear image. The operating principles are introduced, and the experiments are performed and discussed. The concept in this paper can also be extended to design other optical components for modulating direction of light.

Morphological control and switchable photoluminescence responses of silica nanoparticles-modified polymer-dispersed liquid crystal composite films

An electro-optic tunable device is fabricated by the incorporation of silica nanoparticles as a dopant into polymer-dispersed liquid crystal composite film followed by UV curing through polymerisation-induced phase separation process. These silica-modified fibrous aggregates of polydimethylsiloxane provide stability to the nematic liquid crystal molecules. The interaction between dispersed silica nanoparticles and modified polymer network improves the polymer/liquid crystal interface, which was successfully analysed through scanning electron microscopy. It also controlled the birefringence in nematic liquid crystal droplets and provided optical stability to the off-state (opaque) scattering of an electro-optic device. The electrical tuning of photoluminescence intensity during the stage triggering from ‘Switch OFF state’ to ‘Switch ON state’ shows dependence on the morphology of composite films. It can find out potential applications in electrically switchable shutters in display market.

Polarisation switching and molecular relaxation behaviour of anthraquinone dye-dispersed polymer-stabilised ferroelectric liquid crystal composites

Guest–host polymer-stabilised ferroelectric liquid crystal (GH-PSFLC) composite films have been prepared with dispersion of small concentration (0.1, 0.25 and 0.5 wt%) of anthraquinone blue dye in PSFLC host matrix via a polymerisation-induced phase separation (PIPS) process. The variation in alignment and size of twisted fibril has been observed in the optical textures of the guest–host composites with different wt/wt ratio of anthraquinone dye. The electrical and dielectric properties of PSFLC mixture and its guest–host derivatives are studied. Our results showed that an optimum amount of dye concentration (0.1 wt%) enhances the dielectric permittivity as well as the spontaneous polarisation of the GH-PSFLC material in the SmC* phase.

Investigation of liquid crystal dispersion and dielectric relaxation behavior in polymer dispersed liquid crystal composite films

Dispersion dynamics in composites of PMMA-BA and LC E44 were investigated using dielectric relaxation spectroscopy. Morphological studies have shown the homogeneous distribution of LC droplets in the polymer matrix. The outcome was deduced in terms of shape and size of LC droplet, interfacial charge-layer effect, glass transition temperature of composites and miscibility of LC in polymer. The temperature dependent dielectric relaxation spectra have been studied. It was observed that the intensity of Maxwell–Wagner interfacial polarization peak varies with respect to the applied temperature. The high-frequency relaxation process seems to be the Debye-type behavior due to dipolar rotation around the long molecular axis.