Polymer Stabilized Cholesteric Texture Research Articles

Flexible bistable polymer stabilised cholesteric texture light shutter display

ABSTRACT Bistable cholesteric liquid crystal displays meet various needs such as energy saving, long image storage time, and no backlight; however, their dense polymer network affects the electro-optical performance. In this work, polymer-stabilised cholesteric texture (PSCT) films with polymer spacer columns were prepared by two-step polymerisation using photomask. The effects of crosslinker content and mask polymerisation time on the morphology of the polymer spacer columns and the optoelectronic properties of the PSCT films were investigated. The results suggested that the film showed bistable performance and the formation of polymer spacer columns helped to optimize the contrast ratio of the sample without sacrificing response time. The cyclic experiment indicated that the optimized bistable PSCT film showed good stability. The adhesion strength of the PSCT film to the substrate was essentially the same as that of commercial PDLC. The simple operability and reusability of the process method make it a practical solution for the preparation of bistable PSCT films.

Liquid crystal-polymer composites switchable windows for radiant energy flow and privacy control

Global warming is becoming a more and more severe crisis for humans. One way to resolve the concern is to reduce energy consumption. Smart switchable windows for office and residential buildings and vehicles can help reduce energy consumption. An ideal smart window should be able to control radiant energy flow and privacy. We investigated the capability of switchable windows based on liquid crystal/polymer composites, such as polymer dispersed liquid crystal (PDLC), polymer stabilized liquid crystal (PSLC), and polymer stabilized cholesteric texture (PSCT), to control the privacy and radiant energy flow. Through a systematic study, we identified methods to improve their capabilities. We demonstrated that PDLC and PSCT windows of sufficient thick film thickness can control both privacy and energy flow.

Performance improvement for compressive light field display with multi-plane projection

Conventional compressive light field (CLF) displays reconstructing three-dimensional (3D) scenes generally use stacked liquid crystal displays (LCDs). However, the low transmittance of LCD limits the number of stacked layers (usually three) and the image quality. In this paper, the realization of the CLF display with multi-plane projection is proposed by using polymer stabilized cholesteric texture (PSCT) shutter and digital micro-mirror devices (DMDs). Benefitting from high transmittance (>80%) and fast response time (≤1ms) of PSCT shutter, the proposed system provides an opportunity to increase the number of physically stacked layers while preserving high brightness, which could achieve a large depth of field (DOF) and high-fidelity 3D image. Limited by the maximum refresh rate of DMD, the relationship between the gray scale and the layered number is analyzed and optimized to minimize the deviation between reconstructed light field and target light field. To improve the quality of reconstruction, the chromatic aberration due to the wavelength of incident light is investigated and compensated. In addition, the three-dimensional matrix mapping method is presented to convert decomposed images into binary images efficiently, which realizes the high-speed and real-time processing of massive display data. To verify the feasibility of the proposed system, a prototype was implemented and photographs were captured from different viewpoints. With the experimental results, the system was confirmed to have a potential for both 3D display and augmented reality (AR) applications.

Thermo-Chromic Response of Polymer Stabilized Cholesteric Liquid Crystal for Thermal Imaging

Cholesteric liquid crystal (Ch-LC) exhibits many remarkable optical properties due to formation of a macroscopic helical structure. A low amount of monomer (5wt.%) is dispersed into cholesteric liquid crystal and get polymerized under UV radiations to form polymer stabilized cholesteric texture (PSCT). The thermo-chromic response made this device suitable for the developing applications in thermal imaging. Temperature based measurements of PSCT exploits the key property of some polymer stabilized cholesteric liquid crystals (PSCLC) to reflect definite colors at specific temperatures. The selective color of PSCT texture shifts with raise in temperature from 30oC to 85oC, which can be utilized in thermal imaging applications.

Glasses-free 3-D visualization with multi-layered transparent cholesteric films.

Fabrication of a three-dimensional (3D) device with volume-filling autostereoscopic imagery provides a unique solution to the accommodation-convergence mismatch problem in a conventional stereoscopic 3D display. We demonstrate a volumetric 3D display consisting of a stack of sequentially-driven transparent cholesteric films that illuminate every point in the display volume to generate a synthetic 3D image. Transparent cholesteric films comprise of the reverse-mode polymer-stabilized cholesteric texture (R-PSCT) that exhibits > 85% transmittance in its off-state (Grandjean texture) and <15% transmittance in its on-state (focal-conic texture). The polymer network in the R-PSCT is formed with the mixture of reactive monomers: RM6 and RM257. The electro-optical measurements show a strongly influence of concentration of each reactive monomer in the total mixture on the optical contrast and driving voltage of R-PSCT films. Hence, we optimize the composition of reactive monomers in R-PSCT to achieve a low driving voltage, high optical contrast and high electro-mechanical stability. Furthermore, we fabricate a multi-surface and a see-through volumetric 3D display prototype that consists an optical element with 15 R-PSCT films that are sequentially-switched with a microcontroller and operated at 250 Hz. A high-speed DLP projector is used to project a time-multiplexed series of two-dimensional images that are used to build the multi-planar volumetric images.

Fabrication Process of a Reverse Mode Polymer-Dispersed Liquid Crystal using UV Curing

We propose a multi-plane display based on polymer stabilized cholesteric texture (PSCT) Liquid Crystal. The idea of a multi-plane display has shown progress in solving the vergence-accommodation conflict with the eye-brain system. Nowadays new emerging technologies such as the Augmented Reality (AR) and Virtual Reality (VR) share that problem. VR and AR wearable displays, work using stereoscopic 3D glasses, which push the vergence-accommodation conflict. The advantage of the UV-curing method to create a polymer network is the ease to use it on normal lab environments. This method can achieve acceptable response time for a transparent-scattered state on a LC cell, which is needed for a multi-plane display. On this work, we are explaining the fabrication process to create such PSCT LC cell.

51‐2: Multi‐image Plane Display based on Polymer‐stabilized Cholesteric Texture

A multi‐image‐plane display based on cascaded switchable polymer‐stabilized cholesteric texture (PSCT) screens is demonstrated. The unique features of our PSCT screens are twofold: transmittance is 98.2% at voltage‐off state and switching time is around 1 ms. Potential applications include wearable virtual reality, augmented reality, and other head‐mounted displays.

Regulation and control of polymer network deformation in reverse-mode polymer-stabilised cholesteric texture

ABSTRACTBy simulating the dynamic response processes of reverse-mode polymer-stabilised cholesteric texture (PSCT) via double exponential rise/decay model, the deformation of polymer networks were quantitatively characterised. The polymer network deformation is shown to be controlled by regulating monomer concentration and the applied electric field. Increased monomer concentration facilitates the production of polymer fibrils of a higher polymer molecular weight while suppressing distortion of the polymer network. Decreased polymer network deformation assists in the decrease of the undesired hysteresis phenomenon while also demonstrating a shorter field-off response time of PSCT; however, the trade-off is increased operation voltage and decreased contrast ratio. The observed results provide useful guidelines for future PSCT material and device optimisations.

Characterisation and effect of polymer network deformation in reverse-mode polymer-stabilised cholesteric texture

ABSTRACTIn reverse-mode polymer-stabilised cholesteric texture (PSCT), the dynamic response is derived from local director reorientation governed by dielectric coupling effect/self-assembly and polymer network deformation. A double exponential rise/decay model is proposed to investigate the underlying physical mechanisms. Through simulation of the transient rise and decay processes, the polymer network deformation in PSCT can be quantitatively evaluated. Less deformation and faster restoration speed of the polymer network can suppress hysteresis. These results provide useful guidelines for future PSCT fabrication and performance optimisation.

Electrically controllable smart window with greyscale based on polymer-stabilised cholesteric texture films

ABSTRACTThe study reports a novel liquid crystal (LC) film that can be applied on the transmissive substrates or stuck on existing casement window to upgrade the shield. The shadow area and transmittance can be adjusted according to the condition of the outer sunshine. The window is energy saving for which maintains the transmittance after a once-off operation of pulse amplitude modulation (PAM) electric driving. Such a film can be applied in smart curtain, display frame edge and other transmissive electro-optical devices.

聚合物稳定胆甾相滤色液晶光阀的显示研究

聚合物稳定胆甾相滤色液晶光阀的显示研究

螺旋扭曲力常数对常黑聚合物稳定胆甾液晶光电性能的影响

螺旋扭曲力常数对常黑聚合物稳定胆甾液晶光电性能的影响

54.3: PSCT for Switchable Transparent Liquid Crystal Displays

We developed a switchable diffuser for transparent liquid crystal displays. The diffuser is based on polymer stabilized cholesteric texture (PSCT) light shutter. It can be switched between a transparent state and a milky scattering state by applying voltages. The transmittance of the transparent state is near 90%. The reflectance of the scattering state is higher than 30%. We also developed a transparent ADS display with the PSCT, which has excellent viewing angle.

Cell gap effects on domain size and electro-optical properties of normal-mode polymer-stabilised cholesteric texture

The effects of cell gap on the electro-optical properties of normal-mode polymer-stabilised cholesteric texture (PSCT) have been investigated. In this study, the size of the domain and electro-optical properties of PSCT are analysed as a function of the thickness of the cells. Increasing cell gap helps to improve the contrast ratio, but the threshold voltage would increase simultaneously. The scanning electron microscopy indicates that the polymer networks are tightened with increasing cell gap. A denser polymer network leads to smaller domain size, higher effective electric field and decreased field-off response time.

Thickness dependence of the electro-optical properties of reverse-mode polymer-stabilised cholesteric texture

The cell gap dependence of the electro-optical properties of reverse-mode polymer-stabilised cholesteric texture has been investigated. In this study, the morphology and electro-optical properties were analysed as a function of the thickness of the cells. The scanning electron microscopy indicates that the polymer networks become tighter with the decrease of cell gap. Increasing cell gap can improve the contrast ratio exponentially, while the threshold voltage increases linearly. The field-off response time increases, which is ascribed to the decreasing elastic force between the polymer network and the LC molecules.

Submillisecond-Response Light Shutter for Solid-State Volumetric 3D Display Based on Polymer-Stabilized Cholesteric Texture

This paper presents a solid-state volumetric 3-D display system utilizing 20 LC light shutters as a display module, which provides viewers with true depth cues. The electro-optic properties of light shutters based on normal-mode PSCT were investigated. The device shows a field-on transmittance of 86.2%. When applied an operation voltage of 100 V at 28 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C, the response time is 540 μs for switching-on and 180 μs for switching-off, which is suitable for the solid-state volumetric 3-D display. The stability, reliability, and repeatability of the device have also been characterized.

Synthesis and Application of a Novel Liquid Crystal Monomer 1,4-di-[4-(3-acryloyloxyhexyloxy)benzoyloxy]-2-methyl Benzene

A novel liquid crystal monomer 1, 4-Di-[4-(3-acryloyloxyhexyloxy) benzoyloxy]-2-methyl benzene (LCM) was synthesized and characterized by 1H NMR, differential scanning calorimetry (DSC) and polarized optical microscopy (POM). LCM possesses liquid crystal phase between 68 to 124 °C. A f-ast response polymer stabilized cholesteric texture (PSCT) film was prepared based on LCM, and t-he response time was less than 1 ms, which can be applied in true 3D display. In addition, the morp-hology of the polymer network was investigated by scanning electron microscope (SEM).

聚合电场波形对聚合物稳定胆甾相液晶光电性能的影响

聚合电场波形对聚合物稳定胆甾相液晶光电性能的影响

The influence of helical twisting power on the electro-optical properties of reverse-mode polymer-stabilised cholesteric texture

Helical twisting power (HTP), an important parameter of the chiral dopant, was reported to have great influence on the electro-optical properties of reverse-mode polymer-stabilised cholesteric texture (PSCT). In this study, chiral dopants with different HTPs were used to prepare PSCT with the same pitch length. The effect of HTP on the morphology and electro-optical properties of PSCT was investigated. The scanning electron microscopy indicates that the polymer networks become tighter with the increase of HTP. It was found that the threshold voltage increases and field-off response time reduces, which is ascribed to the increasing elastic force between the polymer network and the LC molecules.

聚合网络的锚定作用对聚合物稳定胆甾相液晶光电性能的影响

Polymer-stabilized cholesteric texture(PSCT) samples were prepared by means of polymerization induced phase separation.The electric property of PSCT can be improved by adjusting curing time,which results in the control of the elastic force between polymer networks and liquid crystal molecules.It was indicated that extending the polymerization time can improve the degree of polymerization of monomer,thereby enhancing the anchoring force of polymer networks,whereas has little influence on the morphology of polymer networks. In a normal-mode PSCT,polymer networks are arranged perpendicular to the base plate, which is conducive to the formation of a nematic phase induced by a electric field.With enhancing anchoring effect,low threshold(saturated) voltage,high closed transmittance,low contrast ratio,slow response,and big hysteresis width can be observed.