Liquid Crystal Polymer Composites Research Articles

Enhanced mechanical properties of polyphenylene sulfide and liquid crystal polymer composites by interfacial bonding capacity of graft‐modified graphene oxide and glass fibers

AbstractThe aim of this study is to broaden the potential applications of polyphenylene sulfide (PPS) by incorporating graphene oxide (GO)‐grafted glass fiber (GF) to enhance the mechanical properties of liquid crystal polymer (LCP)/PPS composites. The surface of GF was modified using γ‐Aminopropyltriethoxysilane (KH550), allowing for the grafting of GO. Subsequently, GO‐GF/LCP/PPS composites were prepared through extrusion injection molding. The properties of the composites were evaluated using scanning electron microscopy, differential scanning calorimetry, and thermogravimetric analysis. The findings indicate that the interfacial adhesion between GF and composites is significantly improved with the addition of GO, The mass fractions of GO used were 0.1%, 0.5%, and 0.7%. The incorporation of GO‐grafted GF proves to be an effective approach in enhancing the tensile and flexural strengths of LCP/PPS composites. Additionally, a reduction in wear volume and tribological coefficient is observed compared to composites without GO‐treated GF. Notably, when the GO content is 0.5 wt%, the mechanical properties of the composites show significant improvement, with a 50% increase in impact strength compared to the composite without GO, and a decrease in friction coefficient from 0.28 to 0.22.

Optimization of the Domain Size in Stressed Liquid Crystals

The distributions of orientational and translational order parameters in liquid crystal polymer composites are studied using the methods of molecular-statistical physics. A model is considered in which the composite consists of liquid crystal (LC) domains separated by flat polymer sheets. The perturbation of the orientational and translational order parameters, which is caused by an arbitrary flat polymer sheet in a planar LC layer, is estimated. The effective distance over which this disturbance propagates is estimated. It is shown that it is proportional to the square root of the splay elastic constant of LC. It has been shown that in certain temperature ranges the polymer can induce a more ordered liquid crystal phase near itself (smectic phase inside of nematic phase and nematic phase – inside of isotropic liquid phase). In this case, the orientational order parameter of LC near the polymer can be significantly higher than far from it, and the “perturbation” of the order parameters can propagate over a distance of up to several micrometers with a sharp peak at a distance of the order of one micrometer. Based on the original theory, the methods have been proposed for optimizing the sizes of domains in stressed liquid crystals obtained by mechanical treatment in liquid crystal polymer composites.

Aging Mechanism and Lifetime Prediction of Glass Fiber Reinforced Liquid Crystal Polymer Composite under Thermal and Oxidative Conditions

AbstractDevelopment of fifth‐generation technology leads to a growing demand for materials with exceptional thermal property, mechanical strength, and low dielectric loss. However, ensuring the broad application of such materials by comprehensively investigating their aging mechanisms and service lifetimes remains a challenge. In this work, we have developed a glass fiber (GF) reinforced liquid crystal polymer composite (GF/LCP) and conducted a thorough exploration of its aging mechanism, behavior, and service lifetime under thermal and oxidative conditions. On the basis of the general Arrhenius model, the composite maintains a high level of functionality for a remarkable 18 years at 150 °C and 1.5 years at 200 °C. Despite the extremely high thermal resistance of GF/LCP composite, the LCP matrix exhibits localized brittle fracture, and the main chains still undergo gradual degradation to generate phenolic groups, which ultimately leads to severe pulverization and mass loss. However, a high degree of connection maintenance between GF and LCP components is still reserved. This work provides a valuable reference for the reliable application of 5G materials under thermal and oxidative conditions.

Optofluidic tunable broadband distributed Bragg reflector based on liquid crystal polymer composites.

A dynamically reconfigurable liquid crystal (LC) photonic device is an important research field in modern LC photonics. We present a type of continuously tunable distributed Bragg reflector (DBR) based on LC polymer composites modulated via a novel optofluidic method. LC-templated DBR films are fabricated by photopolymerization under visible standing wave interference. The influences of the incident angle, incident light intensity, and content of ethanol as a pore-forming additive on the reflection behavior are discussed in detail. Then, the LC-templated DBR films are integrated into microfluidic channels and reversibly refilled by different organic solvents. The reconfigurable characteristics of optofluidic DBRs were demonstrated by changing the average refractive index (RI) of the mixed liquids and adjusting the flow rates, resulting in the dynamic and continuous variation of the reflection band within a specific visible light band. It is anticipated that the prototype optofluidic LC device will hopefully be applied to some specific scenarios where conventional means of regulation, such as electric, optical, and temperature fields, are unsuitable and possibly boost the development of microfluidic analysis techniques based on structural color.

Orientation behavior and thermal conductivity of liquid crystal polymer composites based on Three-Dimensional printing

Liquid Crystal Polymer (LCP) / hexagonal boron nitride (BN) composites are manufactured bythree-dimensional (3D)printing approach. The results confirm that 3D printing can build up LCP bulk material with highly aligned nematic domains along the printing path. Also, BN can be orderly arrangement in matrix, exhibiting the same oriented direction as LCP molecules. The degree of orientation of BN is relevant to its lateral dimension. BN with a lateral size of 50 um in LCP matrix has a much higher degree of orientation compared with BN with a lateral size of 0.5 um and 5um. The well-ordered arrangement of BN and aligned LCP result that all of the printed sample has high thermal conductivity. The printed neat LCP bulk has a thermal conductivity 0.74 W m−1 K−1 parallel to the printing path direction, being filled with 20% mass fraction of BN, it can reach to 1.77 W m−1 K−1.

Оптический гистерезис в композитах на основе полимер - нематический жидкий кристалл при одноосной деформации

An experimental setup for studying the phenomenon of optical hysteresis in polymer-liquid crystal composites with controlled surface adhesion under uniaxial deformation is presented. It has been shown experimentally that in polymer - liquid crystal composites based on a nematic liquid crystal (NLC) 4-cyano-4N-heptylbiphenyl (7CB), the phenomenon of optical hysteresis can be observed under uniaxial deformation. The results of this work can be applied as an element of static memory for recording and long-term storage of information, switches of bistable states.

Research progress of electric controlled switchable glass based on liquid crystal-polymer composite

Research progress of electric controlled switchable glass based on liquid crystal-polymer composite

Fabrication and Analysis of Sepiolite/Glass Microcapsules/Liquid Crystal Polymer Composites.

Liquid crystal polymer (LCP) composites filled with sepiolite and glass microcapsules were prepared by melt compounding. The composites were extruded using a twin-screw extruder and injection-molded. The objective of this study is to check a possibility of producing a polymeric composite with a low dielectric constant. Physical characteristics of the composites, such as morphological, rheological, mechanical, and electrical properties were analyzed. In particular, the glass microcapsule-reinforced LCP composites showed a significant improvement in lowering the dielectric constant due to its high air content. Additionally, sepiolite could act as an effective filler to improve the mechanical properties of the composites.

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.

Fast copolymer network liquid crystals for tunable birefringence colors.

A fast-switching, tunable color filter was found in a copolymer network liquid crystal (LC), which was in situ generated in a conventional LC test cell with parallel aligned glass plates and investigated with polarized light. Polarization filters were used to convert the tunable optical phase retardance of the test cells to birefringence colors as is always possible in a LC test cell with carefully adjusted cell gap and effective birefringence. The cell gap of the samples could be adjusted to a value of 9 μm, which is not easily possible in a polymer LC composite without creating defects. In these samples, the typical pastel colors seen frequently in birefringent samples could be avoided. The transmittance spectra were recorded and converted to CIE 1931 color coordinates, which showed that the colors seen had a reasonable distance to the white point. The electro-optic switching times of the samples were investigated: Fast responses of t on +t off <5 ms were found, which is an impressive speed for tunable birefringence colors in LCs and LC composites. Upon increasing addressing voltages, a blueshift of the peak seen in the transmittance spectra was observed. The samples consisted of copolymer network LC, generated from a reactive mixture with mesogenic monomer and nonmesogenic comonomer. The tunable color was seen selectively in samples with dodecyl acrylate as comonomer. The experiments show how even a straightforward electro-optic experiment still can result in unexpended findings, which may expand the use of LC composites in nondisplay applications. The polymer morphology in samples with a larger cell gap was investigated with scanning electron microscopy, and interdefect distances of ≈40 μm were found. The appearance of defects in test cells with a cell gap of 9 μm could be avoided because the cell gap was much smaller than the measured interdefect distances in test cells with a larger cell gap.

High-diffraction-efficiency Fresnel lens based on annealed blue-phase liquid crystal–polymer composite

ABSTRACTWe demonstrated a relatively simple and effective method to fabricate a periodically isolated polymer wall of blue-phase liquid crystal Fresnel lens (BPLCFL) by employing a single-masking process of the ultraviolet (UV) irradiation, leading to excellent photopolymerisation-induced phase separation between blue -phase liquid crystal (BPLC) molecules and UV-curable monomers. Nevertheless, some uncured monomers would inherently reside in the BPLC-rich area and slightly inhibit the BPLC molecules realigned under the external electric field. To enhance the optical properties of the polymer-wall BPLCFL considerably, a novel technique for fabricating a pure BPLC zone is proposed that successfully expels the residual monomers from the BPLC volume using a thermal annealing process. Experimental results show that the maximum diffraction efficiency reaches ~36%, which approaches the theoretical limit of ~41%. Consequently, the annealing technique to purify phase-separated composite films has a strong potential to construct the BPLCFL in light of polarisation-free applications.

Effect of Yttrium Oxide Nanoparticles on the Diffraction Efficiency of Holographic Polymer-liquid Crystal Gratings

Electro-optical properties of the holographic and polarization holographic diffraction gratings formed in polymer-liquid crystal composites doped with Y2O3 nanoparticles are considered. The effect of impurities on the diffraction efficiency and operated electric field is shown. The diffraction efficiency of doped holographic diffraction gratings decreases, whereas the diffraction efficiency of polarization diffraction gratings increases. Doping with nanoparticles leads to a decrease in the operated electric field.

Stability of Laser-Patterned Electrode Compositions

Electrodes can be created with maskless metallization of Cu tracks ablated with laser direct structuring on the surface of a Cu–liquid-crystal polymer composite. The composition of these electrodes may not be stable in a corrosive environment, such as an electrolyte, which is needed to use these structures as conductometric sensors. We have evaluated five different electrode compositions in a low corrosive environment and found electroless palladium–immersion gold to be the most stable. The other electrode compositions have pinholes in the metal layers enabling metal migration and local galvanic corrosion. We also investigate the effect of CO2 snow jet cleaning on the electrodes and its relationship with the electrode composition stability. The CO2 snow jet cleaning leads to smoother electrode surfaces. A smooth electrode surface will have fewer imperfections and therefore less metal migration and galvanic corrosion.

A roll-to-roll process for multi-responsive soft-matter composite films containing CsxWO3 nanorods for energy-efficient smart window applications.

This work provides a roll-to-roll processed flexible multi-responsive smart film containing tungsten bronze nanorods and a phase-separated liquid crystal-polymer composite, which can reversibly control the passage of visible light in response to temperature, an electric field and near infrared light, and also screen the heat rays from 800 nm to 2500 nm.

Investigation of the Effect of Yttrium Oxide Nanoparticles Doped with Cerium and Neodymium on Electro-Optics of Liquid Crystal Polymer Composites

Morphology and properties of liquid crystal polymer composites doped with inorganic nanoparticles are described. These composites comprised nematic liquid crystal 5CB, polyvinyl acetate, and nanoparticles of oxides (Y2O3, CeO2:Y2O3, and Nd2O3:Y2O3). Nanopowders were synthesized by the laser method of vaporization of a solid target under CO2-laser or fiber ytterbium laser irradiation. The effect of oxides on the electro-optical properties of the composites and times of response to an electrical pulse is investigated. It is shown that incorporation of CeO2:Y2O3 nanopowder in liquid crystal polymer composites affects the decrease of the control field and the increase of light transmission in an electric field stronger than incorporation of Nd2O3:Y2O3 nanoparticles.

Liquid crystal composites doped with inorganic nanoparticles for recording of polarization holographic gratings

The properties of polarization holographic gratings formed in liquid crystal polymer composites doped with inorganic nanoparticles (SiO2, ZnO, Al2O3, and Y2O3) are considered. The effect of these additives on the phase transition temperature of liquid crystals of polarization gratings, diffraction efficiency, and driving voltage is demonstrated.

Dielectric Properties of Liquid Crystal Polymer Composites with High Thermal Conductivity

Liquid crystal (LC) polymer, composited with inorganic filler, has a broad application prospect in electronic and electrical industry. In this research, permittivity (εr) and dielectric loss tangent (tanδ) of LC composites under different temperatures and frequencies were investigated, and activation energies were calculated and analyzed. At low temperatures and high frequencies, LC composites exhibited well dielectric properties. εr changed a little (3.6~4.0) in temperature range of-60°C~160°C when frequency was higher than 10Hz, but increased sharply when temperatures was higher than 100°C and frequency was lower 10Hz. The tanδ increased sharply with increasing temperature when temperatures was higher than 100°C and frequency was lower than 102Hz, and when frequency was above 102Hz, the value of tanδ changed gently (10-3~10-2). The peak of tanδ would translate to higher frequencies direction with increasing temperature in tanδ-frequency curve, and to higher temperatures direction with increasing frequency in tanδ-temperature curve. Activation energy is calculated by fitting the peak of the imaginary of the electric modulus, and activation energy is 0.43eV in low temperature and 1.59eV in high temperature.

Three-dimensional vector holograms formed in twisted-nematic azo-dye-doped polymer liquid-crystal composite

Three-dimensional (3D) vector holograms have been formed in twisted-nematic (TN) azo-dye-doped polymer liquid crystal (LC) composites whose director is gradually rotated around the thickness direction in the initial state. Polarization states of diffracted beams were rotated in accordance with the twist angle, and the diffraction efficiency depended markedly on the incident angle. We confirmed that the 3D director distributions corresponded to the polarization modulation caused not only by light interference and the propagation in the LCs but also by the initial orientation of the LCs. In order to explain the observed properties a theoretical model of the periodic reorientation distribution in TN LCs was presented. The Jones matrix method is used to describe the interference of two polarized light beams in the anisotropic media. Then the finite-difference time-domain method was applied to analyze the diffraction properties of the 3D vector holograms recorded in the model medium.

Three-dimensional vector recording in polarization sensitive liquid crystal composites by using axisymmetrically polarized beam.

Three-dimensional anisotropic structures were fabricated by a recording axisymmetrically polarized beam in azobenzene (azo)-dye doped liquid crystal polymer composites. Polarization and wavefront modulation properties of fabricated anisotropic structures are investigated by experimentally and theoretically analyzing the diffraction properties. Photo-induced anisotropic structures would be utilized to generate singular light waves, such as optical and polarization vortices.

Оптические методы формирования высокоструктурированных полимерно-жидкокристаллических композитов

Оптические методы формирования высокоструктурированных полимерно-жидкокристаллических композитов