Liquid Crystal Polymer Film Research Articles

A compact, highly sensitive optical fiber temperature sensor based on a cholesteric liquid crystal polymer film

Liquid crystals (LCs) are commonly used to enhance the temperature sensitivity of fiber optic temperature sensors. Most studies utilized non-polymerizable LC-filled optical fibers, which suffer from drawbacks such as complex structure, low temperature detection capability, and narrow measurement range. In this study, a temperature sensor with a wide measurement range, high sensitivity, and simple fabrication process was proposed by directly integrating polymerizable cholesteric liquid crystal (CLC) films onto the end face of optical fibers. The effects of various components in CLC on temperature response were investigated and the temperature sensor fabricated from sample Ⅱ-4 exhibited the best performance. It can detect temperatures ranging from 30 to 270 °C. Within the range of 30–150 °C, its sensitivity is 381 pm/°C, while from 150 to 270 °C, the sensitivity increases to 879 pm/°C. Moreover, it achieves a rapid response time of just 300 ms. Its small size allows monitoring in confined spaces, expanding LC sensor applications.

Photo‐Active Soft Actuator Enabling Dynamic Manipulable Lenses with Surface Reshaping

AbstractManipulable lenses with tunable focal length have garnered great attention due to their unique advantages including strong adjustability, low power consumption, fast response times, and ease of integration. However, in the context of advancing intellectualization, weight reduction, and miniaturization of imaging systems, mere focal length adjustment is no longer sufficient. Herein, an innovative method is introduced for creating a dynamic light manipulable (DLM) lens with surface reshaping. This breakthrough is accomplished through the collaborative integration of a medium lens with an actuator based on photo‐active liquid crystal polymer (LCP) film, where the deformation of the photo‐active LCP film can be arbitrarily controlled by meticulously designing the orientation distributions of liquid crystal (LC) mesogens within the film. The lens with three distinct surfaces, including quasi‐cone, paraboloid, and 3 × 3 paraboloid array, are demonstrated with infrared stability, robust fatigue resistance, long natural recovery time, outstanding thermal stability, and excellent solvent resistance, further confirming the feasibility of the lens application in tunable display, imaging, infrared optics, and other systems. This work holds the promise of paving the way for a new generation of imaging systems.

Thin film resonant metasurface absorbers using patch-based arrays on liquid crystal polymer substrates for centimeter-wave applications

This paper reports the design and development of thin-film resonant absorbers for narrowband and multiband operation in the frequency regions centered at 10 GHz. The structure of the resonant metasurface absorber (RMA) is based on a liquid crystal polymer (LCP) thin-film spacer with a copper patch array on the front surface and un-patterned copper film on the back surface of the LCP film. The design and simulation works were carried out using full-wave analysis of the RMA characteristics. The copper-based periodic patch array acts as a metasurface. The perfect RMA for a given LCP film thickness can be obtained through impedance optimization by adjustment of the dimensions of the lattice periods. The electric and magnetic field distributions were studied. The resonant film absorber based on a 100 μm thick LCP film has an electrical thickness of λ/300 at 10 GHz. The experimental work was conducted using a narrowband RMA prototype consisting of 11×11 cells. The measured result of the resonant absorption is at 10.1 GHz, which is in close agreement with the design frequency of 10 GHz. For multiband functionality, double- and quad-band film resonant absorbers have been designed based on a coplanar supercell utilizing the superposition of the resonance effect. The LCP film-based absorbers have the potential to be used in EM shielding and sensing applications in centimeter-wave applications.

Amplified Circularly Polarized Luminescence Behavior in Chiral Co-assembled Liquid Crystal Polymer Films via the Strategic Manipulation of Chiral Inducers.

One of the most important factors for the future application of circularly polarized luminescence (CPL) materials is their high dissymmetry factors (gem), and more and more studies are working tirelessly to focus on increasing the gem value. Herein, we chose an achiral liquid crystal polymer (LC-P) and two chiral binaphthyl-based inducers (R/S-3 and R/S-6) with different substitution positions (3,3' positions for R/S-3 and 6,6' positions for R/S-6) to construct chiral co-assemblies and explored their induced amplification CPL behaviors. Interestingly, after the thermal annealing treatment, this kind of chiral co-assembly (R/S-3)0.05-(LC-P)0.95 can emit a superior CPL signal (|gem| = 0.31 and λem = 424 nm), which achieves about 13-fold signal amplification in the spin-coated film, compared to (R/S-6)0.1-(LC-P)0.9 (|gem| = 0.023 and λem = 424 nm). This is because (R/S-3)0.05-(LC-P)0.95 could further co-assemble to form a more ordered arrangement LC state and generate regular helix nanofibers than that of (R/S-6)0.1-(LC-P)0.9. This work provides an efficient method for synthesizing high-quality CPL-active materials through the strategic manipulation of the structure of chiral binaphthyl-based inducers in chiral co-assembled LCP systems.

Broadband directional filter in multilayer liquid crystal polymer films at W-band

In this work, a four-port directional filter (DF) with a broad passband and low reflection is proposed at the W-band, which comprises three unit filters at 92, 95, and 97 GHz, cascaded in series. Each unit consists of two microstrip lines in the top circuit layer for signal input and output, two pairs of apertures in the middle ground layer for directional coupling, and one square loop in the bottom layer as a selective resonator. By sweeping the working frequencies of the three units and optimizing the phase delays between them, the proposed filter achieves a 3-dB bandwidth as broad as 16%, an insertion loss of 2.5 dB at 95 GHz, and an out-of-band rejection of −28 and −23 dB at 80 and 110 GHz, respectively. The corresponding reflection attenuation is larger than 9.6 dB from 60 to 105 GHz. To verify our design, a prototype is fabricated and characterized, and its experimental data are consistent with the simulation. This work significantly expands the bandwidth of DFs and may find many applications in frequency division multiplexing and high-gain wireless systems.

Strong Circularly Polarized Luminescence Promoted by AIE-active Chiral Co-assemblies in Liquid Crystal Polymer Films.

Recently, extensive works have focused on increasing the dissymmetry factors (glum) of various circularly polarized luminescence (CPL) materials, which is one of the most important factors for future applications of CPL. Herein, we designed a chiral co-assembled liquid crystal polymer (LCP) PTZ@R/S-PB2, which was prepared by chiral binary co-polymer (R/S-PB2) doped with achiral phenothiazine derivation dye (PTZ). For comparison, ternary co-polymerized LCP (R/S-PT) was synthesized by co-polymerizing with mesogenic monomer, chiral monomer and emissive monomer. Both PTZ@R/S-PB2 and R/S-PT showed aggregation-induced emission (AIE) properties. Interestingly, the CPL signals of both PTZ@R/S-PB2 and R/S-PT were reversed and amplified after thermal annealing treatment. The |glum| values of the co-assembled PTZ@R/S-PB2 were up to 0.13 at a 32 nm thickness, which was 5.4 times that of R/S-PT (|glum|=0.024). This is due to PTZ@R/S-PB2 could form more orderly chiral co-assembly structures. Noticeably, increasing the LCP film thickness could further improve the glum value, and the maximum glum of PTZ@R/S-PB2 could be enhanced to +0.91/-0.82 at a 220 nm thickness.

Dynamic Shape Change of Liquid Crystal Polymer Based on An Order‐Order Phase Transition

AbstractLiquid crystal actuators conventionally undergo shape changes across an order‐disorder phase transition between liquid crystal (LC) and isotropic phases. In this study, we introduce an innovative Liquid Crystal Polymer (LCP) actuator harnessing an order‐order LC phase transition mechanism. The LCP film is easily stretchable within the LC phase, facilitated by the π–π stacking of phenyl groups serving as robust physical crosslinking points, and thereby transforms to a stable monodomain structure. The resultant monodomain LCP actuator shows a distinctive reversible dynamic shape change, exhibiting extension followed by contraction along the LC director on cooling. The extension is propelled by the reversible smectic C to smectic A phase transition, and the contraction is attributed to the re‐entry to the smectic C phase from smectic A phase. Thermal annealing temperature determines this peculiar dynamic shape change, which occurs during both heating and cooling processes. This pivotal attribute finds manifestation in gripper and flower‐shaped actuators, adeptly executing grabbing and releasing as well as blooming and closure motions within a single thermal stimulation. In essence, our study introduces an innovative approach to the realm of LCP actuators, ushering in a new avenue for the design and fabrication of versatile and dynamically responsive LCP actuators.

Dynamic Shape Change of Liquid Crystal Polymer Based on An Order-Order Phase Transition.

Liquid crystal actuators conventionally undergo shape changes across an order-disorder phase transition between liquid crystal (LC) and isotropic phases. In this study, we introduce an innovative Liquid Crystal Polymer (LCP) actuator harnessing an order-order LC phase transition mechanism. The LCP film is easily stretchable within the LC phase, facilitated by the π-π stacking of phenyl groups serving as robust physical crosslinking points, and thereby transforms to a stable monodomain structure. The resultant monodomain LCP actuator shows a distinctive reversible dynamic shape change, exhibiting extension followed by contraction along the LC director on cooling. The extension is propelled by the reversible smectic C to smectic A phase transition, and the contraction is attributed to the re-entry to the smectic C phase from smectic A phase. Thermal annealing temperature determines this peculiar dynamic shape change, which occurs during both heating and cooling processes. This pivotal attribute finds manifestation in gripper and flower-shaped actuators, adeptly executing grabbing and releasing as well as blooming and closure motions within a single thermal stimulation. In essence, our study introduces an innovative approach to the realm of LCP actuators, ushering in a new avenue for the design and fabrication of versatile and dynamically responsive LCP actuators.

Geometric phase-encoded stimuli-responsive cholesteric liquid crystals for visualizing real-time remote monitoring: humidity sensing as a proof of concept

Liquid crystals are a vital component of modern photonics, and recent studies have demonstrated the exceptional sensing properties of stimuli-responsive cholesteric liquid crystals. However, existing cholesteric liquid crystal-based sensors often rely on the naked eye perceptibility of structural color or the measurement of wavelength changes by spectrometric tools, which limits their practical applications. Therefore, developing a platform that produces recognizable sensing signals is critical. In this study, we present a visual sensing platform based on geometric phase encoding of stimuli-responsive cholesteric liquid crystal polymers that generates real-time visual patterns, rather than frequency changes. To demonstrate this platform’s effectiveness, we used a humidity-responsive cholesteric liquid crystal polymer film encoded with a q-plate pattern, which revealed that humidity causes a shape change in the vortex beam reflected from the encoded cholesteric liquid crystal polymers. Moreover, we developed a prototype platform towards remote humidity monitoring benefiting from the high directionality and long-range transmission properties of laser beams carrying orbital angular momentum. Our approach provides a novel sensing platform for cholesteric liquid crystals-based sensors that offers promising practical applications. The ability to generate recognizable sensing signals through visual patterns offers a new level of practicality in the sensing field with stimuli-responsive cholesteric liquid crystals. This platform might have significant implications for a broad readership and will be of interest to researchers working in the field of photonics and sensing technology.

Controllable Circularly Polarized Luminescence with High Dissymmetry Factor via Co-Assembly of Achiral Dyes in Liquid Crystal Polymer Films.

Circularly polarized luminescence (CPL) materials are highly demanded due to their great potential in optoelectronic and chiroptical elements. However, the preparation of CPL films with high luminescence dissymmetry factors (glum) remains a formidable task, which impedes their practical application in film-based devices. Herein, a facile strategy to prepare solid CPL film with a high glum through exogenous chiral induction and amplification of liquid crystal polymers is proposed. Amplification and reversion of the CPL appear when the films are annealed at the chiral nematic liquid crystalline temperature and the maximal glum up to 0.30 due to the enhancement of selective reflection. Thermal annealing treatment at different liquid crystalline states facilitates the formation of the chiral liquid phase and adjusts the circularly polarized emission. This work not only provides a straightforward and versatile platform to construct organic films capable of exhibiting strong circularly polarized emission but also is helpful in understanding the exact mechanism for the liquid crystal enhancement of CPL performance.

Photo-responsive nanoporous liquid crystal polymer films for selective dye adsorption.

Photo-responsive nanoporous polymer films (AZOF-R(NC6)) have been developed by a template method based on a hydrogen-bonding supramolecular liquid crystal (LC) and a light-sensitive azobenzene LC crosslinker in this work. Anionic nanopores were obtained after the removal of template NC6 using KOH solution. The AZOF-R(NC6) demonstrates charge-selective dye adsorption and the maximum adsorption capacity for Rh6G is 504.6 mg g-1. The AZOF-R(NC6) film without UV light treatment shows a 32% higher adsorption capacity for Rh6G than the AZOF-R(NC6) film treated with UV light within the initial 10 min. In addition, UV light can trigger the release of the adsorbed dye from the polymer film due to the pore size change arising from the trans-cis isomerization. Besides, the used polymer film can be effectively regenerated using a HCl solution. Such functional polymer films with highly ordered nanopores and photo-responsive properties hold great promise in selective adsorption and mass separations.

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.

Optical properties and nanosecond laser damage characterization of liquid crystal polarization gratings

Liquid crystal polarization gratings (LCPGs) possess unique optical properties and therefore are widely used in laser systems. Therefore, developing our understanding of the laser damage resistance of LCPGs is critical for future high-intensity laser applications. In this study, the LCPGs (Λ = 8 μm) were fabricated from liquid crystal polymer (LCP) films with photo-alignment technology, which had a small-angle (∼7.51°) diffraction order with high diffraction efficiency (∼92 %) under chiral polarized incidence at 1064 nm. The diffraction efficiency and polarization of each diffraction order were determined by the polarization of the incident light. The damage characteristics of the LCPGs were investigated using a chiral polarized nanosecond laser at 1064 nm in a one-on-one test. The laser-induced damage thresholds (LIDTs) of left-handed circular polarization (LHCP) and right-handed circular polarization (RHCP) were 8.0 J/cm2 and 8.5 J/cm2, respectively. For comparison, the LIDTs of S-polarization and P-polarization were 7.8 J/cm2 and 8.4 J/cm2, respectively. All the damage occurred at the interface between the LCP layer and the substrate when the laser fluence was near the LIDT, and the damage morphology was observed with a scanning electron microscope (SEM), including flat pits, cracks, and bumps at the edge of the pits. The results indicate that the LIDTs and damage morphology of the LCPGs were insensitive to the polarization of the irradiation. The electrical effects of differently polarized irradiation on the LCPGs were simulated using the finite element method (FEM). The electric field distribution was symmetrical under irradiation by LHCP and RHCP lasers. However, the distribution of the electric field under different linearly polarized irradiation conditions were distinct. Based on these findings, we believe that the contribution of chiral polarized irradiation to the damage was consistent and that the LIDTs were similar. This study has important implications for the application and development of LCPGs in high-intensity laser systems.

Synergistic Effect of Fluorination and Molecular Orientational Order on the Dielectric Properties of Low-κ Liquid Crystal Polymer Films

Synergistic Effect of Fluorination and Molecular Orientational Order on the Dielectric Properties of Low-κ Liquid Crystal Polymer Films

Laser-Assisted Structuring of Graphene Films with Biocompatible Liquid Crystal Polymer for Skin/Brain-Interfaced Electrodes.

The work presented here introduces a facile strategy for the development of flexible and stretchable electrodes that harness the robust characteristics of carbon nanomaterials through laser processing techniques on a liquid crystal polymer (LCP) film. By utilizing LCP film as a biocompatible electronic substrate, control is demonstrated over the laser irradiation parameters to achieve efficient pattern generation and transfer printing processes, thereby yielding highly conductive laser-induced graphene (LIG) bioelectrodes. To enhance the resolution of the patterned LIG film, shadow masks are employed during laser scanning on the LCP film surface. This approach is compatible with surface-mounted device integration, enabling the circuit writing of LIG/LCP materials in a flexible format. Moreover, kirigami-inspired on-skin bioelectrodes are introduced that exhibit reasonable stretchability, enabling independent connections to healthcare hardware platforms for electrocardiogram (ECG) and electromyography (EMG) measurements. Additionally, a brain-interfaced LIG microelectrode array is proposed that combines mechanically compliant architectures with LCP encapsulation for stimulation and recording purposes, leveraging their advantageous structural features and superior electrochemical properties. This developed approach offers a cost-effective and scalable route for producing patterned arrays of laser-converted graphene as bioelectrodes. These bioelectrodes serve as ideal circuit-enabled flexible substrates with long-term reliability in the ionic environment of the human body.

Technological method of increasing photosensitivity in photochromic liquid crystal polymer films

Technological method of increasing photosensitivity in photochromic liquid crystal polymer films

A styrylpyrene‐containing liquid crystal polymer for photoinduced crosslinking

AbstractPhotoresponsive polymers have attracted increasing attention. Herein, we designed and synthesized a photoresponsive liquid crystal polymer (LCP). The LCP was prepared through the copolymerization of a styrylpyrene‐containing photoresponsive monomer and a monomer containing mesogen 4‐cyanophenyl benzoate. Gel permeation chromatography (GPC) curve and 1H nuclear magnetic resonance (1H NMR) spectrum confirmed that the LCP was successfully synthesized. Thermogravimetric analysis and differential scanning calorimetry curves showed that the LCP had high thermal stability, with a decomposition temperature at 5% weight loss of 305°C, and Tg and Ti of 46 and 128°C, respectively. Polarized optical microscopy studies suggested that thermal annealing promoted the orientation of the LCP films. Model compounds containing styrylpyrene units showed photo‐controlled dimerization. Furthermore, the dimerization of the styrylpyrene units could control the crosslinking densities in the LCP, thereby regulating the network structures and properties. These properties demonstrate that the LCP is a promising photoresponsive material.

Quadri-Dimensional Anti-counterfeiting Flexible Label Programmed by a Photoresponsive Liquid Crystal Polymer Film

Creating flexible materials with multi-dimensional security holds great promise for anti-counterfeiting labels in food, currency, and pharmaceuticals, but it is proven extremely challenging. Herein, we propose a photoresponsive liquid crystal polymer (LCP) film by incorporating polymerizable photoswitch into commercial LCP with ultraviolet (UV) light exposure. Reversible photochromism can be observed between light- and dark-red under UV and visible light irradiation alternatively, accompanying by variation of fluorescence intensity. In addition, a series of photonic microstructures are written on the flexible LCP film by taking advantage of the predefined patterned light. A quadri-dimensional anti-counterfeiting flexible label, featuring photochromism, fluorescence, embedded microstructures, and optical diffraction is constructed with the assistance of photoresponsive LCP film. This strategy represents a beneficial step toward flexible anti-counterfeiting materials, which enhances the secure level for practical product engineering applications.

Lasing chirality control of thin-film defect-mode lasers based on cholesteric liquid crystal polymer mirrors

This work investigates the emission chirality of a chiral distributed Bragg reflector (DBR) laser, which is composed by incorporating an isotropic medium containing laser dye between two cholesteric liquid crystal polymer films. The emitted laser showed different ratios of circularly polarized states corresponding to different pitch numbers of the chiral mirror. Through Berreman matrix numerical calculations and experimental results, we validated the variations of the emission chirality coupling in the defect resonance mode as a function of pitch numbers, as well as the effect of the defect layer thickness on the wavelength and mode number of the emitted laser. We also observed the cone-shape emission and examined the threshold of the lasing. The results successfully demonstrated the realization of DBR laser with controllable orthogonal circular polarization ratios in the emitted laser light. These results offer considerable potential for the development of micro-laser sources with different emission chirality and wavelengths for various applications.

Geometry Controlled Oscillations in Liquid Crystal Polymer Films Triggered by Thermal Feedback.

Light-induced oscillatory behavior of liquid crystal polymer network (LCN) films has been demonstrated by several researchers in the past decade. Similarly, oscillations in LCN films under constant thermal stimulus have been reported recently, although the mechanism and the factors that govern the oscillatory behavior are not well understood. In this work, we study the dynamics of self-sustained oscillations exhibited by LCN films under a constant thermal stimulus through experiments and simulations. Geometrically asymmetric films such as a right triangle and an equilateral triangle are obtained from a twisted nematic square film. A multiphysics computational framework using the finite element method is developed to simulate the oscillatory behavior of the LCN films kept on a hot plate. The framework accounts for a coupling between heat transfer and mechanical deformations during the oscillations. Small temperature fluctuations (≈ 1 °C) coupled with gravity induced torque are shown to drive the oscillatory behavior at a specific plate temperature. We show for the first time that self-sustained oscillations can also be achieved in symmetric shapes, such as square films, by creating a thickness tapering between two opposite edges. The frequency of the oscillations is found to be in the range of 0.5 to 2.5 Hz for different geometries studied. The oscillation temperature depends on the mean thickness, size, and thickness profile of the films. As a possible application, we demonstrate a thermally actuated optical chopper using the oscillatory response of the films.