Polymer Dispersed Liquid Crystal System Research Articles

Preparation of polymer dispersed liquid crystal doped with bilayer nanofiber membranes and phase‐change microcapsule coating for enhanced infrared modulation

AbstractThe effective manipulation and regulation of infrared (IR) radiation represent significant advancements in the realm of liquid crystal applications. In this investigation, the synergistic integration of nanofiber membranes and phase change microencapsulated film with polymer dispersed liquid crystal (PDLC) layers was employed for IR modulation. To obtain the excellent electro‐optical properties of PDLC composite films, the ratio of the PDLC system, the thickness of the nanofiber membrane, and the concentration of phase‐change microcapsules were meticulously regulated, and the polymer network morphology of the PDLC films was analyzed to achieve a high contrast ratio (162.72) of PDLC composite films. The fabricated PDLC composite devices show excellent IR shielding efficiency of 15% in the presence of doped nanofiber membranes and phase change microencapsulated films. Notably, patterned nanofiber layers and phase‐change microcapsule coating were obtained by template electrospinning, resulting in patternable PDLC composite film devices.

ATO and Cs0·33WO3 loaded bilayer nanofiber membrane doped polymer dispersed liquid crystals for infrared shielding

Liquid crystals possess a wide range of applications in modulating infrared (IR) light and have drawn great interest especially in near-infrared shielding and passive radiative cooling. Here, a composite structure containing polymer dispersed liquid crystals (PDLC) with antimony doped tin oxide and cesium tungsten oxide loaded bilayer nanofiber membranes with IR shielding properties is proposed. The composite film and the blank liquid crystal cell are irradiated simultaneously under IR light, and the temperature detector shows that the average temperature drop of the PDLC composite film in the scattered state and the fully transparent state over the blank sample are 6.8 °C and 4.1 °C, respectively. More importantly, the dynamic IR shielding properties of the composite films are demonstrated by patterning the nanofiber films. In addition, this organic/inorganic hybrid PDLC system not only modulates IR light, but also exhibits excellent electro-optical properties, aging resistance, flexural stability (1000 cycles), and tensile resistance. The composite film combines ease of preparation with compatibility for industrial-scale roll-to-roll or continuous manufacturing processes, highlighting the great potential of PDLC for applications in tunable optical heat transport materials.

Voltage‐Driven Molecular Orientation with Optical Synergy in Rare Earth Doped Polymer Dispersed Liquid Crystals

AbstractAchieving reversible large‐span photoluminescence regulation still faces difficulties due to limitations in the design or preparation conditions of related materials. Herein, a universal strategy that combines voltage‐driven molecular orientation with optical synergy between rare earth (RE) doped materials and polymer dispersed liquid crystals (PDLC) is proposed to achieve large‐span reversible opto‐electrically synergistic induced multi‐response photoluminescence regulation. The obtained Eu(tta)3phen/PDLC composites can exhibit different emission colors reversible transform from purple to purplish‐pink depending on the excitation wavelength and the applied electric voltage. The interaction between PDLC and Eu(tta)3phen is analyzed and the field distribution of internal microstructures is simulated using the finite‐difference time‐domain method, providing a theoretical basis for the voltage‐dependent photon interactions. The potential applications of Eu(tta)3phen/PDLC composites for anticounterfeiting is suggested by demonstrating a proof‐of‐concept anticounterfeiting system based on the composites. The strategy of opto‐electrically synergistic induced multi‐response photoluminescence regulation, with general applicability, can be easily extended to other RE doped materials and PDLC systems, opening up new possibilities for photoluminescence regulation research.

Rheological Properties Study of Polymer Dispersed Liquid Crystals Doped by SiO2 Nanoparticles

The present report discusses the development of a novel nano-composite using a polymer dispersed liquid crystal (PDLC) and inorganic silicon dioxide (SiO2) nanoparticles. The aim of this work was to investigate the effect of the SiO2 nanoparticles on the rheological properties of the PDLC films. In our research described in this paper SiO2 nanoparticle-doped polymer dispersed liquid crystal films were made from a mixture of ethylene glycol phenyl ether methacrylate (EGPEMA) pre-polymer, 4-Cyano-4′-pentylbiphenyl (5CB) liquid crystals (LC) and SiO2 nanoparticles by the polymerization induced phase separation (PIPS) process. Doping the PDLC systems with SiO2 improved the rheological properties of these materials; the percolation (network formation) observed reflected the good interfacial adhesion between the nanoparticles, the polymer matrix and the LC. On the other hand, a decrease in the storage modulus (G′) and loss modulus (G″) of the PDLC systems after addition of the SiO2 nanoparticles confirmed their high flexibility and low crystallinity. A slight increase in G′ at 0.05 wt.% SiO2 resulted in the good mechanical strength of the doped PDLC. The viscoelastic behavior of the doped and undoped PDLC systems was confirmed at high frequencies. Thermal characterization by differential scanning calorimetry (DSC) showed a decrease in the glass transition temperature (Tg) of the PDLC with 0.05 wt.% of SiO2 nanoparticles, which showed that we had a more flexible material.

Towards Femtoscan-Assisted Analysis of Liquid Crystal Self-Organization on Different Polymer and Glass Surfaces for Lab-on-a-Chip and Lab-on-a-Dish Applications, Including Optofluidic and Flexoelectric Ones

<span lang="EN-US">In this paper, starting with an introductory review of the applications of liquid crystals and polymer-dispersed liquid crystal systems in (bio)sensors and microfluidics, the possibilities of visualizing self-organization products of liquid crystalline media or field-induced instabilities of liquid crystalline systems are considered. In particular illustrated cases, it is proposed to use FemtoScan software-containing metrological complexes to visualize instabilities in liquid crystalline systems and products of self-organization in liquid crystalline media.

Effects of thiol‐ene click reaction on morphology and electro‐optical properties of polyhedral oligomeric silsesquioxane nanostructure‐based polymer dispersed liquid crystal film

AbstractPolymer dispersed liquid crystals (PDLCs) have lit a flash of interest due to the distinctive property of electrically controlled switching. However, too high‐driving voltage associated with porous polymer networks always limit their wider range of applications. Herein, we reported a PDLC system containing LCs, 2,2′‐(Ethylenedioxy)diethanethiol (DET) with thiol groups, cage‐like nanostructure acrylic polyhedral oligomeric silsesquioxane (KH570‐POSS) and KH570‐SiO2 nanoparticle modified by acrylic groups. The cage‐like KH570‐POSS microstructure was injected to the polymer matrix when KH570‐POSS reacted with DET via thiol‐ene click reaction. The morphological results demonstrated that the droplet size increased with the higher content of DET due to the decrease of the crosslink between the acrylic groups in KH570‐POSS, which results in a less dense of polymer network and thus make the LC droplets easier to be driven in the electric filed. Then, a silica‐based nanoparticle KH570‐SiO2 modified by acrylic groups was introduced into the system. The results indicated that KH570‐SiO2 could replace partial KH570‐POSS to form the polymer network via thiol‐ene click reaction, which increased the compatible ability of SiO2 nanoparticles in the as‐made film. The contrast ratio was increased to 165 when there was nearly 5 wt% content of KH570‐SiO2. Besides, the driving voltage was reduced by almost 60% and the sample could be fully driven by 30 V which is lower than the safe voltage (36 V). This study opens a route for the preparation of commercial PDLC films by thiol‐ene click reaction, enabling the creation of low‐voltage‐driven smart windows.

Dynamically color-changing polymer-dispersed liquid crystals containing ionic liquid for smart window applications

ABSTRACT In this work, we report a bifunctional dynamically colour-changing polymer-dispersed liquid crystals (PDLCs) for smart windows by doping a supporting electrolyte ionic liquid into the conventional PDLC system. The transmittance spectra were used to measure the electrically colour-changing properties of the system, while the electro-optical curves were employed to examine the electrically switchable performances. The SEM was used to observe the surface morphology of the polymer microstructure. The result obtained from this work suggested that such device could obtain four independent states under different electric fields. The initial state was opaque and colourless due to the randomly dispersed liquid crystal droplets. The transparent and colourless state was obtained as a result of reorientation of liquid crystal under alternative current (AC) electric field. The opaque and green state was achieved under direct current (DC) electric field owing to the oxidation reaction in the system. Besides, the transparent and green state was realised via applying DC and AC electric field simultaneously or in steps. The convenience and simplification of switching between the four states enable the system to provide some interesting applications for smart windows.

Fabrication of epoxy/thiol polymer-based polymer-dispersed liquid crystals containing a catalyst with multi-amine structures

Accelerators are usually used to promote the thermal curing of epoxy/thiol mixtures and help to improve the preparation efficiency of epoxy-based polymer-dispersed liquid crystals (PDLCs). However, some accelerators may cause serious yellowing of the resultant products and their catalytic effect is also limited. In this work, a commercial compound with multi-amine structures is employed as the catalyst to prepare epoxy/thiol polymer-based PDLC films. The experimental results indicate that this catalyst not only does not lead to the serious yellowing problem of the PDLC films, but also can obviously improve the thermal curing rate between epoxy and thiol monomers in the PDLC system. The effects of curing times and curing temperatures on the electric-optical performance and the polymer morphology of the epoxy-based PDLCs are studied systematically. A flexible epoxy-based PDLC film, which can be completely driven by a voltage below the safety voltage (36 V), is also realized successfully.

TiO2 doped polymer dispersed and stabilised liquid crystal smart film with high contrast ratio, low driving voltage and short response time

ABSTRACT Due to the switchability between transparent and light-scattering states, polymer-dispersed liquid crystals (PDLCs) are widely used as smart windows, flexible display devices, projectors and other devices. In this work, we propose a new composite system containing TiO2 nanoparticles (NPs), liquid crystals and polymer that have low driving voltage, high contrast ratio (CR) and quick response ability. Distinguishing from the traditional PDLC system, the coexisting structure of vertically oriented polymer fibres (VOPFs) inside the porous polymer matrix was constructed and the TiO2 nanoparticle (NP) after functionalisation was introduced. It was found that the introduction of an appropriate amount of functionalised TiO2 NPs can effectively improve the electro-optical properties of the composite system. This new system provides a new idea for solving the compatibility problem of inorganic particles and organic matter.

The Electro-optical study of Al2O3 nanoparticles doped polymer dispersed liquid crystal films

ABSTRACT The electro-optical characteristics of nanoparticles-doped polymer dispersed liquid crystals (PDLCs) have been investigated for display applications. The PDLC samples were obtained by polymerisation induced phase separation of the nematic liquid crystal LC-nanoparticles-prepolymer mixtures under UV illumination with a constant intensity. The effect of Al2O3 nanoparticles doping on the PDLC system was studied. It was seen that the electro-optical characteristics of PDLC were dependent on the amount of Al2O3 nanoparticles used. The effect of morphology on the electro-optical properties was examined, and the experimental results indicated that the driving voltage was affected considerably by the amount of Al2O3 nanoparticles. The results showed that the nanoparticles concentration can be optimised to obtain promising electronic materials with a minimum threshold for display applications.

Doping white carbon black particles to adjust the electro-opticical properties of PDLC

ABSTRACT Polymer-dispersed liquid crystal (PDLC) is a possible active matrix transparent display technology due to its high transparency, good visibility, and low-power consumption. This paper examined the morphology of polymer-dispersed liquid-crystal materials (PDLCs), which show great potential for display applications. The materials were blends of an eutectic nematic liquid-crystal mixture and a UV-cross-linkable polymeric matrix. White carbon black nanomaterials with high surface adsorbability, high purity, and good stability are ideal materials for the driver circuit of the PDLC display. The influence of the ratio between polymerised monomers and between polymerised monomers and liquid crystals on the electro-optical properties of PDLC system had been studied. We explored the doping of white carbon black nanomaterials in the liquid crystal polymer systems. To achieve this, we have taken advantage of the liquid crystal electro-optical effect experimental instrument to study a series of electro-optical parameters of PDLC, using also additional information on the nanodroplet size and shape distribution provided by SEM images of the PDLC cross-section.

The Effect of Curing Temperature on the Morphology and Electro-Optical Properties of a Flexible UV-Cured Polymer Dispersed Liquid Crystal (PDLC)

In this work, the experimental data on flexible PDLC films at the industrial scale and the effect of cure temperature (Tc) on the morphology and electro-optical properties of a UV-cured PDLC system via polymer-induced phase separation (PIPS) method were studied. Under constant UV radiation intebsity and thickness, the morphological parameters such as dimension, number density, and volume fraction of the phase-separated liquid crystal droplets as well as the optical transmissions and switching voltages as a function of cure temperature were determined. The effect of cure temperature on the morphology and electro-optical properties of UV-cured PDLC films were analyzed.

High-Performance Polymer Dispersed Liquid Crystal Enabled by Uniquely Designed Acrylate Monomer.

The widespread electro–optical applications of polymer dispersed liquid crystals (PDLCs) are hampered by their high-driving voltage. Attempts to fabricate PDLC devices with low driving voltage sacrifice other desirable features of PDLCs. There is thus a clear need to develop a method to reduce the driving voltage without diminishing other revolutionary features of PDLCs. Herein, we report a low-voltage driven PDLC system achieved through an elegantly simple and uniquely designed acrylate monomer (A3DA) featuring a benzene moiety with a dodecyl terminal chain. The PDLC films were fabricated by the photopolymerization of mono- and di-functional acrylate monomers (19.2 wt%) mixed in a nematic liquid crystal E7 (80 wt%). The PDLC film with A3DA exhibited an abrupt decline of driving voltage by 75% (0.55 V/μm) with a high contrast ratio (16.82) while maintaining other electro–optical properties almost the same as the reference cell. The response time was adjusted to satisfactory by tuning the monomer concentration while maintaining the voltage significantly low (3 ms for a voltage of 0.98 V/μm). Confocal laser scanning microscopy confirmed the polyhedral foam texture morphology with an average mesh size of approximately 2.6 μm, which is less in comparison with the mesh size of reference PDLC (3.4 μm), yet the A3DA-PDLC showed low switching voltage. Thus, the promoted electro–optical properties are believed to be originated from the unique polymer networks formed by A3DA and its weak anchoring behavior on LCs. The present system with such a huge reduction in driving voltage and enhanced electro–optical performance opens up an excellent way for abundant perspective applications of PDLCs.

The effect of curing temperature and time on morphology and Electro-Optical properties of flexible thermoset polymer dispersed liquid crystal (PDLC) films

In this work, we studied the effect of cure temperature (Tc) and cure time (tc) on the morphology and few electro-optical properties of flexible thermoset PDLC systems by Polymer Induced Phase Separation (PIPS) method. Under a constant thickness, we determined the morphological parameters including dimension, number density and volume fraction of phase separated liquid crystal droplets, as well as optical transmissions and switching voltages as a function of cure temperature and cure time. We analyzed the effect of cure temperature and time on morphology and electro-optical properties in the thermoset PDLC films.

Multiple bio-responsive polymer dispersed liquid crystal composites for sensing applications

Polymer dispersed liquid crystal (PDLC) composites were prepared by the encapsulation of cholesteryl acetate (L-ChAc) in polyvinyl alcohol boric acid (PVAB) by microemulsion technique. The supramolecular and morphological peculiarities of the resulted composites were analyzed by polarized optical microscopy, fluorescence microscopy and scanning electron microscopy respectively. The thermal behavior of the systems was evaluated by differential scanning calorimetry and the surface characteristics in terms of wettability and surface free energy were calculated based on contact angle measurements. Circular dichroism was further used to evidence the chiroptical properties of the studied PDLCs and to have an insight on the potential interactions between the components. The ability of the composites to act as sensors for different blood analytes was preliminary tested by POM. The results indicated that PVAB facilitated a uniform distribution of the cholesteric liquid crystal as micrometric droplets with narrow polydispersity and planar anchoring. The obtained PDLCs proved moderate wettability and they showed a selective responsiveness for L or D sugars, amino acids and DNA. All these results indicated the new polymer dispersed liquid crystal systems as promising materials for biosensors building.

Phase Diagrams of Polymer-Dispersed Liquid Crystal Systems of Itraconazole/Component Immiscibility Induced by Molecular Anisotropy

Liquid crystalline (LC) materials and their nonmedical applications have been known for decades, especially in the production of displays; however, the pharmaceutical implications of the LC state are inadequately appreciated, and the misunderstanding of experimental data is leading to possible errors, especially in relation to the physical stability of medicines. The aim of this work was to study LC phases of itraconazole (ITZ), an azole antifungal active molecule, and for the first time, to generate full thermodynamic phase diagrams for ITZ/polymer systems, taking into account isotropic and anisotropic phases that this drug can form. It was found that supercooled ITZ does not form an amorphous but a vitrified smectic (vSm) phase with a glass transition temperature of 59.35 °C (determined using a 10 °C/min heating rate), as is evident from X-ray diffraction and thermomicroscopic (PLM) experiments. Two endothermic LC events with the onset temperature values for a smectic to nematic transition of 73.2 ± 0.4 °C and a nematic to isotropic transformation at 90.4 ± 0.35 °C and enthalpies of transition of 416 ± 34 J/mol and 842 ± 10 J/mol, respectively, were recorded. For the binary supercooled mixtures, PLM and differential scanning calorimetry showed a phase separation with birefringent vSm persistent over a wide polymer range, as noticed especially for the hypromellose acetate succinate (HAS) systems. Both, smectic and nematic, phases were detected for the supercooled ITZ/HAS and ITZ/methacrylic acid-ethyl acrylate copolymer (EUD) mixtures, while geometric restrictions inhibited the smectic formation in the ITZ/poly(acrylic acid) (CAR) systems. The Flory-Huggins lattice theory coupled with the Maier-Saupe-McMillan approach to model anisotropic ordering of molecules was successfully utilized to create phase diagrams for all ITZ/polymer mixtures. It was concluded that in a supercooled ITR/polymer mix, if ITZ is present in a LC phase, immiscibility as a result of molecule anisotropy is afforded. This study shows that the LC nature of ITZ cannot be disregarded when designing stable formulations containing this molecule.

The physical properties of alkene-terminated liquid crystal molecules/E8 mixture and the electro-optical properties as they doped in polymer-dispersed liquid crystal systems

ABSTRACTEffects of the content of fluorinated alkene-terminated liquid crystal (LC) molecules on the physical properties of the fluorinated alkene-terminated LC/E8 mixture were studied. The morphology and electro-optical properties as they doped in polymer-dispersed liquid crystal (PDLC) films were investigated. The detailed discussion of the obtained results is given. As a result, comparing with the physical properties of the series of LC mixtures with the same content of the analogous fully saturated compounds doped with E8, we find that the birefringence is significantly larger for the LC mixture with the alkene-terminated materials. Both fluorinated alkene-terminated LC molecules and the analogous fully saturated compounds doped with E8 reduce the driving voltage of PDLC films. Moreover, PDLC films with the fluorinated alkene-terminated LC molecules possessed higher contrast ratio and faster response time than that of the PDLC films prepared by adding the same mass fraction of the analogous fully saturated compounds. Thus, the ability to manipulate physical properties of LC mixture and electro-optical properties of PDLC films by changing the LC molecular structures may have future relevance for new LC structures design and applications of PDLC films.

Preparation of polymer-dispersed liquid crystal doped with indium tin oxide nanoparticles

ABSTRACTTo study polymer-dispersed liquid crystal (PDLC) films doped with indium tin oxide (ITO) nanoparticles (NPs), samples were prepared by ultraviolet-initiated polymerisation based on the thiol–acrylate system. Owing to the interaction between PDLC system and ITO NPs, the content and the size of ITO NPs are the main determinants to the microstructure which plays an essential role on the electro-optical and anti-infrared properties of the PDLC films. In the polymer matrix, a novel microstructure consisting of a dense surface, micron-sized meshes and submicron meshes is found to benefit the better performances of the low driven voltage (20.7 V), the relatively high contrast ratio (8.3) and the lowest transmittance(500–2500 nm) on average at about 3.55% with maximum of merely 7.6%. Thus, it lays a solid foundation for the further investigations on the microstructure and the performance of the PDLC films. Meanwhile, it is proved that the PDLC film, improved performance through doping ITO NPs, is promising to be a superior choice in the field of energy-saving.

Fabrication of dye-doped polymer-dispersed liquid crystals with low driving voltage based on nucleophile-initiated thiol-ene click reaction

ABSTRACTDye-doped polymer-dispersed liquid crystal (PDLC) is an attractive material for application in smart windows. We report a novel dye-doped PDLC system with low driving voltage (Vdr) fabricated by nucleophile-initiated thiol-ene click reaction for the first time. The Vdr decreased significantly with the addition of monofunctional monomer. The influences of reaction temperature on the electro-optical properties of PDLC are also investigated in this work.

Preparation of a Thermally Light-Transmittance-Controllable Film from a Coexistent System of Polymer-Dispersed and Polymer-Stabilized Liquid Crystals.

Polymer-dispersed liquid crystal (PDLC) and polymer-stabilized liquid crystal (PSLC) systems are the two primary distinct systems in the field of liquid crystal (LC) technology, and they are differentiated by their unique microstructures. Here, we present a novel coexistent system of polymer-dispersed and polymer-stabilized liquid crystals (PD&SLCs), which forms a homeotropically aligned polymer network (HAPN) within the LC droplets after a microphase separation between the LC and polymer matrix and combines the advantages of both the PDLC and PSLC systems. Then, we prepare a novel thermally light-transmittance-controllable (TLTC) film from the PD&SLC system, where the transmittance can be reversibly changed through thermal control from a transparent to a light-scattering state. The film also combines the advantageous features of flexibility and a potential for large-scale manufacturing, and it shows significant promise in future applications from smart windows to temperature sensors.