Liquid Crystal Films Research Articles

Polymerization strategy for cellulose nanocrystals-based photonic crystal films with water resisting property

Cellulose nanocrystals (CNCs) can form a liquid crystal film with a chiral nematic structure by evaporative-induced self-assembly (EISA). It has attracted much attention as a new class of photonic liquid crystal material because of its intrinsic, unique structural characteristics, and excellent optical properties. However, the CNCs-based photonic crystal films are generally prepared via the physical crosslinking strategy, which present water sensitivity. Here, we developed CNCs-g-PAM photonic crystal film by combining free radical polymerization and EISA. FT-IR, SEM, POM, XRD, TG-DTG, and UV–Vis techniques were employed to characterize the physicochemical properties and microstructure of the as-prepared films. The CNCs-g-PAM films showed a better thermo-stability than CNCs-based film. Also, the mechanical properties were significantly improved, viz., the elongation at break was 9.4 %, and tensile strength reached 18.5 Mpa, which was a much better enhancement than CNCs-based film. More importantly, the CNCs-g-PAM films can resist water dissolution for more than 24 h, which was impossible for the CNCs-based film. The present study provided a promising strategy to prepare CNCs-based photonic crystal film with high flexibility, water resistance, and optical properties for applications such as decoration, light management, and anti-counterfeiting.

Preparation of a double-layer liquid crystal optical shutter with fluorescent properties and its ultraviolet shielding screening properties

ABSTRACT Polymer dispersed liquid crystal (PDLC) films and polymer-stabilised cholesteric liquid crystals (PSCLC) films have been widely applied in smart optoelectronics due to electrical switching properties. In this study, fluorescent dyes were introduced into PDLC films and combined with PSCLC films to invent a new type of optical shutter, and the optimal formulations of each of liquid crystal structural layers were investigated. Then, PDLC anti-counterfeit optical device doped with fluorescent materials were fabricated by UV curing method using polymerisation-induced phase separation. The novel optical shutter could be driven layer by layer at room temperature according to different voltages to realise the switching of three states, namely, off state, PDLC layer-driven, and full-driven (open state). Samples under optimal conditions showed that the new optical shutter could achieve 96.5% UV shielding in the off state and had a long lifetime. The results demonstrate the attractive potential of the new optical shutter for optoelectronic devices and smart curtain applications.

A novel double-layer liquid crystal electro-optic switch and its infrared shielding properties investigation

ABSTRACT In this study, a novel light switch was developed by integrating polymer dispersion liquid crystals (PDLC) and polymer-stabilised cholesteric liquid crystals (PSCLC), leveraging the infrared shielding properties of these two liquid crystal films. The optimal formulation for each layer of the liquid crystal structure was investigated. Subsequently, the effects of light intensity, high temperature, and humidity on the performance of the light switch were examined. This new light switch can be selectively driven layer by layer at room temperature, achieving three states: the off state, PDLC layer-driven state, and full-driven (on state). This functionality serves the purpose of electrogenerated temperature control. Samples under optimal conditions exhibited a 31% enhancement in infrared shielding compared to a single-layer PDLC film. Moreover, the IR shielding rate could be adjusted according to the voltage applied, realising an intelligent temperature-control effect. The results of this study suggest that such bilayer liquid crystal structures hold significant potential for application in electro-optical devices and smart curtain systems.

Preparation and Characterization of Bilayer Polymer-Dispersed Liquid Crystals Doped with Gd2O3 Nanoparticles and Rhodamine B Base Fluorescent Dye.

Using the polymerization-induced phase separation (PIPS) method, bilayer polymer-dispersed liquid crystal (PDLC) films with a PDLC-PVA-PDLC structure were prepared in this work. It was found that all PDLC performance indexes were affected by polymer mesh size after comparing the microscopic morphology and electro-optical properties of samples with different monomer ratios. Gd2O3 nanoparticles and rhodamine B base fluorescent dyes introduced into the bilayer PDLC optimized the samples' electro-optical properties and developed new functionalities. In addition, the bilayer PDLC doped with Gd2O3 and rhodamine B base held excellent progressive driving functions as well as stable durability properties. Samples doped with Gd2O3 nanoparticles and rhodamine B base also produced excellent anti-counterfeiting effects under UV irradiation at different angles, further exploiting the application potential of PDLC.

Preparation and Application of Polymer-Dispersed Liquid Crystal Film with Step-Driven Display Capability.

The realization of multifunctional advanced displays with better electro-optical properties is especially crucial at present. However, conventional integral full drive-based transparent display is increasingly failing to meet the demands of the day. Herein, partitioned polymerization as a novel preparation method was introduced innovatively into polymer-dispersed liquid crystals (PDLC) for realizing a step-driven display in agreement with fluorescent dye to solve the above drawback. At first, the utilization of fluorescent dye to endow the PDLC film with fluorescent properties resulted in a reduction in the saturation voltage of the PDLC from 39.7 V to 25.5 V and an increase in the contrast ratio from 58.4 to 96.6. Meanwhile, the experimental observations and theoretical considerations have elucidated that variation in microscopic pore size can significantly influence the electro-optical behavior of PDLC. Then, the step-driven PDLC film was fabricated through the exposure of different regions of the LC cell to different UV-light intensities, resulting in stepwise voltage-transmittance (V-T) responses of the PDLC film for the corresponding regions. Consequently, under appropriate driving voltages, the PDLC can realize three different states of total scattering, semi-transparent and total transparent, respectively. In addition, the PDLC film also embodied an outstanding anti-aging property and UV-shielding performance, which makes it fascinating for multifunctional advanced display applications.

Bubble lasers can be sturdy and sensitive

Made of liquid-crystal films, the soft, air-filled lasers have stable spectra that shift when the bubbles are squeezed.

Disentangling optical effects in 3D spiral-like, chiral plasmonic assemblies templated by a dark conglomerate liquid crystal.

Chiral thin films showing electronic and plasmonic circular dichroism (CD) are intensively explored for optoelectronic applications. The most studied chiral organic films are the composites exhibiting a helical geometry, which often causes entanglement of circular optical properties with unwanted linear optical effects (linearly polarized absorption or refraction). This entanglement limits tunability and often translates to a complex optical response. This paper describes chiral films based on dark conglomerate, sponge-like, liquid crystal films, which go beyond the usual helical type geometry, waiving the problem of linear contributions to chiroptical electronic and plasmonic properties. First, we show that purely organic films exhibit high electronic CD and circular birefringence, as studied in detail using Mueller matrix polarimetry. Analogous linear properties are two orders of magnitude lower, highlighting the benefits of using the bi-isotropic dark conglomerate liquid crystal for chiroptical purposes. Next, we show that the liquid crystal can act as a template to guide the assembly of chemically compatible gold nanoparticles into 3D spiral-like assemblies. The Mueller matrix polarimetry measurements confirm that these composites exhibit both electronic and plasmonic circular dichroisms, while nanoparticle presence is not compromising the beneficial optical properties of the matrix.

The regulation of electro-optical properties and polymer morphology of polymer-dispersed liquid crystal films with silicon nanostructure

ABSTRACT In this work, the thiol modified silica nanostructures (SiO2-SH) were doped into polymer-dispersed liquid crystal (PDLC) films. The SEM was used to observe the morphology of the polymer microstructure. The electro-optical (E-O) property test was determined by a liquid crystal parameter tester. The SEM images suggested that the SiO2-SH nanoparticles can react with acrylate groups to form the polymer matrix. The saturation voltage decreased by half in the sample when the dosage of the SiO2-SH nanoparticles was 7.5 wt%, which may be due to the reduced anchoring strength of the polymer matrix incorporated with silicon nanoparticles resulting from the lower surface energy and the enhanced steric repulsions of LC droplets and polymer matrix. In addition, the preparation conditions like polymerisation temperatures and UV light intensity also effectively regulated the E-O properties and polymer microstructure of the PDLC film with silica nanostructure. Thus, the results showed that the E-O properties and the polymer morphology of PDLC films with silicon nanostructures can be effectively regulated by doping SiO2-SH nanoparticles and regulating the preparation conditions such as the polymerisation temperature and UV light intensity. This work can provide practical guidance for modulating the properties of PDLC films.

Effects of hydroxylated acrylates on electro-optical performance and adhesion strength of polymer dispersed liquid crystal films

In this study, effects of hydroxylated acrylate monomers that includes both monoacrylate and diacrylate on properties of the as-made polymer dispersed liquid crystal (PDLC) films are explored. The electro-optical response, microstructure and adhesion strength are characterized to compare the influences in detail. It is revealed that hydroxylated acrylate monomers can significantly enhance the adhesion strength in comparison with the non-hydroxylated monomer. Moreover, the hydroxyl group can alter the microstructure of the polymer matrix by affecting the polymerization and phase separation process. Thereby, the electro-optical response of the PDLC film is affected. Additionally, the influences are closely related to the position and concentration of hydroxyl group in acrylate monomers. When the hydroxyl group is located in the α-position or is distant from the reactive site, the improvement is limited. Increasing the concentration of hydroxyl groups by introducing monomers containing multiple hydroxyl groups in one molecule or combining hydroxylated monoacrylate and hydroxylated diacrylate monomers can change the microstructure type and deteriorate the electro-optical performance. By carefully balancing these factors, an optimized PDLC film can be obtained, whose adhesion strength is elevated to about 2.3 times that of the non-hydroxylated film and contrast ratio is improved from 135 to 262. This work is anticipated to provide deeper insights into the role of hydroxylated monomers and offer more possibilities to improve the overall performance of the PDLC films.

High-Performance Organic Narrow Dual-Band Circular Polarized Light Detection for Encrypted Communications and Color Imaging.

Conventional circularly polarized light (CPL) detectors necessitate several optical elements, posing difficulties in achieving miniature and integrated devices. Recently developed organic CPL detectors require no additional optical elements but usually suffer from low detectivity or low asymmetry factor (g-factor). Here, an organic CPL detector with excellent detectivity and a high g-factor is fabricated. By employing an inverted quasi-planar heterojunction (IPHJ) structure and incorporating an additional liquid crystal film, a CPL detector with an outstanding g-factor of 1.62 is developed. Unfavorable charge injection is effectively suppressed by the IPHJ structure, which reduces the dark current of the organic photodetector. Consequently, a left CPL detectivity of 6.16 × 1014 Jones at 640nm is realized, surpassing all of the latest photodiode-type CPL detectors. Adopting a liquid crystal film with adjustable wavelengths of selectively reflected light, the hybrid device achieves narrow dual-band CPL detection, varying from 530 to 640nm, with a half-maximum full width below 90nm. Notably, the device achieves excellent stability of 260 000 on/off cycles without attenuation. To the best of the authors' knowledge, all these features have rarely been reported in previous work. The CPL detector arrays are also demonstrated for encrypted communications and color imaging.

Effects of polarizing film arrangement on the viewing angle of polymer-dispersed liquid crystal films

Polymer-dispersed liquid crystal (PDLC) film is an electrically controlled dimming film in which the orientation of the liquid crystal molecules can be changed by applying an electric field. When the liquid crystals are perpendicular to the PDLC film, the film is transparent. Birefringence occurs after light passes through the liquid crystal molecules, resulting in two beams of light with perpendicular vibration directions. Therefore, PDLC film appears hazy when viewed from the side. In this study, a polarizing film was introduced to reduce the side-view haze, and its influence on the haze at different angles and positions was investigated. Experiment results revealed that aligning the PDLC film along the polarizing film’s absorption axis reduced the haze at all angles. When the polarizing film was attached to each side of the PDLC film and the absorption axis angle of the films was 0∘, a wide-viewing-angle PDLC film was obtained; at a 45∘ tilt, the haze only increased by 0.33%, and at 60∘ it maintained a clear field of view. This may be because only light in the same direction as the absorption axis passed through the film, reducing the amount of light that did not match the polymer refractive index.

Surface effect on the phase separation in thin liquid crystal film as seen from a mean-field approach

The effect of the interplay between attractive nonlocal surface interactions and attractive pair long-range intermolecular couplings on molecular structures of liquid crystals confined in thin cells with flat solid surfaces has been studied. It has been shown, in the framework of the extended McMillan′s mean field theory, that in the confined LC system a complex orientational and translational ordering of molecules can be induced. Several scenarios of the formation of local smectic A, nematic, and isotropic phases have been shown to coexist in a certain temperature range. Due to the nonlocality of the surface interaction, an unexpected complexity of the spatial arrangement of these local phases along the direction of the normal to the surface may exhibit itself.

Light-controllable liquid crystal platform for microparticle oscillations and transport.

Liquid crystal colloids manifest complex motion caused by external stimuli, but tunable and addressable control of microsized objects remains a challenge. This study aims to demonstrate light-driven trapping, transport, and sustained periodic motions of microparticles by employing liquid crystal films as a light-controllable colloidal platform. The diverse motions of microscopic particles result from Marangoni convection coupled with elastic deformations in free-surface liquid crystal films subjected to light beam heating. The specific mode of particle motion, including damped and sustained oscillations, also combined with sustained rotation, is defined by the liquid crystal chirality, particle surface treatment, film thickness, and the power of the tightly focused light beam. The results reveal that free-surface liquid crystals provide a unique platform for the indirect optical manipulation of microscopic objects, paving the way for novel applications in microfluidic tools, particle sorting and transport, micropatterning, and various micromachines.

Coalescence of biphasic droplets embedded in free standing smectic A films.

We investigate micrometer-sized flat droplets consisting of an isotropic core surrounded by a nematic rim in freely suspended smectic A liquid-crystal films. In contrast to purely isotropic droplets which are characterized by a sharp edge and no long-range interactions, the nematic fringe introduces a continuous film thickness change resulting in long-range mutual attraction of droplets. The coalescence scenario is divided in two phases. The first one consists in the fusion of the nematic regions. The second phase involves the dissolution of a thin nematic film between the two isotropic cores. The latter has many similarities with the rupture of thin liquid films between droplets coalescing in an immiscible viscous liquid.

Near room temperature multilevel resistive switching memory with thin film ionic liquid crystals

Multilevel operation of nonvolatile resistive random-access memory devices was demonstrated using thin films of an ionic liquid crystal, 1-dodecyl-3-methylimidazolium tetrafluoroborate ([C12mim][BF4]), as a resistive switching layer.

Visibility of patients and respect for their privacy: reconciling apparently contrary imperatives in the intensive care unit

Rigorous monitoring of vital functions in intensive care requires optimal visibility of patients and their environment. Conversely, respect for privacy is an ethical imperative to respect. Liquid crystal electrical film is a device that can be applied to windows and can take opaque or transparent form on demand. Its use could satisfy the visibility of patients and respect for their privacy.

Preparation and properties of broadband reflective cholesteric-phase liquid crystal films based on chiral and achiral bilayer structures

In this work, N* and N bilayer liquid crystal composite systems were constructed. With the synergistic effect of diffusion and UV-induced photopolymerization, CLC films reflecting over the wavelength range of 1500 nm were prepared.

See-Through Light Field Mixed-Reality Display System Based on Polymer Dispersed Liquid Crystal Film

See-Through Light Field Mixed-Reality Display System Based on Polymer Dispersed Liquid Crystal Film

A blue phase liquid crystal film based on an interpenetrating network and its sensitive humidity response performance

A humidity-responsive blue phase liquid crystal polymer film (alkalized-acrylic-BP) based on an interpenetrating polymer system has been fabricated.

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.