Crystal Polymer Composites Research Articles

Rheology and Processing of High-Strength Liquid Crystal Polymer Reinforced Thermoplastic Composite Materials

Liquid crystal polymer (LCP) composites are presented as lightweight, high-strength, thermoplastic composites. Fumed silica (FS), carbon black (CB), carbon nanostructures (CNS), and boron nitride (BN) added to the polyphenylene sulfide (PPS) increased the viscosity ratio of the PPS to the LCP. PPS filled with 5 wt.% FS was used to optimize injection molding conditions and had a viscosity ratio ranging from 2 to 13. Increasing fill time to 5 s brought about the highest tensile strength of 99 MPa and modulus of 12.5 GPa, while the tool and melt temperatures imparted no significant effect. Mechanical and thermal properties of select LCP materials processed using molding conditions optimized for the experimental materials are presented. Mechanical properties in the crossflow direction were lower than in the flow direction, which could be overcome with tool design and placement of valve gates to tailor the flow patterns. BN filled composites increased the thermal conductivity to a value of 0.26 W/mK at 16 wt.% loading.

Circularly polarised luminescence of cholesteric polymer composite with high concentration of europium complex

ABSTRACT A novel method has been developed for fabricating cholesteric liquid crystal polymer composite containing a luminescent europium complex. It involves creating porous cholesteric polymer networks, introducing the europium complex into the pores and encapsulating it through the UV-induced polymerisation of a nematic diacrylate. The resulting composite exhibits bright red luminescence upon excitation by UV light which is strongly circularly polarised. Such materials have potential applications in display technologies, counterfeit protection and other fields.

Effects of Composition and Polymerization Conditions on the Electro-Optic Performance of Liquid Crystal-Polymer Composites Doped with Ferroelectric Nanoparticles.

The presence of a polymer network and/or the addition of ferroelectric nanoparticles to a nematic liquid crystal are found to lower transition temperatures and birefringence, which indicates reduced orientational order. In addition, the electro-optic switching voltage is considerably increased when a polymer network is formed by in situ polymerization in the nematic state. However, the resulting polymer network liquid crystal switches at similar voltages as the neat liquid crystal when polymerization is performed at an elevated temperature in the isotropic state. When nanoparticle dispersions are polymerized at an applied DC voltage, the transition temperatures and switching voltages are reduced, yet they are larger than those observed for polymer network liquid crystals without nanoparticles polymerized in the isotropic phase.

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.

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-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.

Ultra-fast responsive colloidal\u2013polymer composite-based volatile organic compounds (VOC) sensor using nanoscale easy tear process

There is an immense need for developing a simple, rapid, and inexpensive detection assay for health-care applications or monitoring environments. To address this need, a photonic crystal (PC)-based sensor has been extensively studied due to its numerous advantages such as colorimetric measurement, high sensitivity, and low cost. However, the response time of a typical PC-based sensor is relatively slow due to the presence of the inevitable upper residual layer in colloidal structures. Hence, we propose an ultra-fast responsive PC-based volatile organic compound (VOC) sensor by using a “nanoscale easy tear (NET) process” inspired by commercially available “easy tear package”. A colloidal crystal-polydimethylsiloxane (PDMS) composite can be successfully realized through nanoscale tear propagation along the interface between the outer surface of crystallized nanoparticles and bulk PDMS. The response time for VOC detection exhibits a significant decrease by allowing the direct contact with VOCs, because of perfect removal of the residual on the colloidal crystals. Moreover, vapor-phase VOCs can be monitored, which had been previously impossible. High-throughput production of the patterned colloidal crystal–polymer composite through the NET process can be applied to other multiplexed selective sensing applications or may be used for nanomolding templates.

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.

Orientation effects in 2–2 composites based on single- or polydomain ferroelectric relaxor crystals

Effective physical properties are considered in 2–2 ferroelecric relaxor crystal–polymer composites with poly- or single-domain crystal components. The important role of orientation effects in forming the severe hydrostatic response, high piezosensibility, and large anisotropy of the electromechanical coupling factors is shown.

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 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.

Enhancement of birefringence of liquid crystals with dispersion of poly (n-butyl methacrylate) (PBMA)

In this work, we have reported the temperature dependence of birefringence for pure liquid crystals (LCs) and liquid crystal-polymer composite (LC-PC) systems. The enhancement of the electro-optical performances is higher in LC with poly (n-butyl methacrylate) polymer. The temperature dependence of the birefringence (Δn) were determined from the transmitted intensity. Dielectric study of pure LC system and LC-PC system has also been presented as a function of frequency. The observed results may be attributed to the occurrence of polymeric domains (chains) formed in LCs. The complete study reveals that the use of polymeric materials in nematic LCs is effective to improve the response in phase shifters devices.

Negative dispersion of birefringence of smectic liquid crystal-polymer composite: dependence on the constituent molecules and temperature.

We investigated the dependence of the negative dispersion of birefringence of smectic liquid crystal-polymer composites on the constituent molecules and temperature. The dispersion of birefringence was significantly varied from positive dispersion to negative dispersion by the change of the relative fraction of the constituent monomers. For the temperature dependence of the dispersion, a composite with more fraction of monomers located at the inter-layer space showed a wider temperature range of the negative dispersion of birefringence.