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Viewing-angle-switching film based on polymer dispersed liquid crystals for smart anti-peeping liquid crystal display
Abstract
In this paper, the viewing-angle-switching (VAS) films based on polymer dispersed liquid crystals (PDLCs) were fabricated and the optical properties of the VAS films were studied. The VAS films based on PDLC films can exhibit electrically switchable viewing-angle properties, and the films showed a narrow viewing angle under no electric field and presented a wide viewing angle under electric field (24 V). Furthermore, the smart anti-peeping liquid crystal display (LCD) containing the VAS film based on PDLC film also displayed the electrically switchable viewing-angle performance and the corresponding mechanism was discussed. The results demonstrated both the anti-peeping effect and electrically switchable view-angle effect of the as-fabricated VAS film, promising potential applications in intelligent optical films and novel information displays.
... Smartphones, laptops, and other products for electronic information displays have developed rapidly and become an essential part of our work and life [1]. To pursue a better display effect, the wide viewing angle, high luminance, and high reliability are used in electronic displays, bringing visual feast and enjoyment to users [2]. ...
... Zhou et al. reported a novel film with switchable viewing angle that can make the viewing angle of a liquid crystal display (LCD) electrically switchable between ±30 • and ±60 • , which has potential applications in highquality LCDs [3]. He et al. fabricated a viewing-angle-switching film with the AP effect and electrically switchable viewing angle effect [1]. So far, most studies have focused on the physical structure of the film and its influence on screen luminance [1 3 5], but there is little research on the influence of the film on visual performance. ...
... Inspired by the application of PDLC in the display field, these materials have been rapidly developed in recent years. It has been expanded to other areas beyond displays [4,5] and smart windows [6][7][8][9], such as anti-peep [10], quantum dot films [11,12], and switchable glazing [13][14][15]. In addition, PDLC has been applied in other fields to obtain new composite materials, such as less-energy-hungry buildings [16,17], sensing [18,19], and energy storage [20]. ...
In this paper, the bilayer polymer-dispersed liquid crystals possessing a PDLC-PVA-PDLC structure were prepared by integrating two monolayer PDLCs. The effect of the polymer mesh size on the electro–optical properties of a bilayer PDLC was investigated by comparing the micro-morphology and electro–optical curves under different polymerization conditions. In addition, the impact of doping MoO2 nanoparticles with surface modification on the comprehensive performance of the bilayer PDLC was further researched. The contrast ratio of the bilayer PDLC prepared under the optimal conditions was improved by more than 90% and still maintained excellent progressive driving performance. Therefore, the development of a bilayer PDLC with optimal electro-optical properties will significantly enhance the technological prospects for the application of PDLC-based devices in smart windows, displays, and flexible devices.
... Several technologies have been developed to control the viewing angle of displays, including privacy films with louvers [6], polymer-dispersed LC (PDLC) [7][8][9], and sub-pixel approaches [10]. However, these technologies encounter various challenges. ...
We propose a switchable privacy display with liquid crystals for co-driver displays (CDDs) in vehicles. The display minimizes driver distraction while allowing the co-driver to enjoy infotainment content. By combining electrically controllable birefringence (ECB) and hybrid-aligned nematic (HAN) cells, we control the viewing angle of the display. Our device achieves an operating angle of 30°, effectively blocking the driver’s view while providing a wide viewing angle for the co-driver. It maintains excellent transmittance properties in privacy and public modes, with symmetric luminance characteristics. The versatility of the proposed display extends to various technologies like LCDs, OLEDs, and micro-LEDs. This switchable privacy display has the potential to enhance driver safety and infotainment experiences in vehicles.
... The investigation of various physical properties of PDLC and their possible potential applications were performed by many researcher groups. Mikhail et al. studied the electrically controllable polarizers using polymer dispersed nematic liquid crystal [16], E. P. Pozhidaev et al. studied the electrically controlled light scattering using PDLC in the visible and near-infrared ranges [17], Zemin He et al. fabricated viewing-angle-switching film based on PDLC and investigated its optical properties [18], Zeng Liang et al. prepared ZnO nanoparticles doped PDLC from a mixture of UV curable liquid polymer and investigated morphological and electro-optical properties [19], Haonan Lin et al. investigated the morphologies, electro-optical and mechanical properties of methacrylate monomers on PDLC [20], We have investigated optical and thermal properties of PDLC [21]. Many other researchers investigated the effect of polymer on NLC but as per our literature survey the effect of different concentration of polymer on optical and electrical properties of NLC is not yet investigated . ...
Polymer dispersed liquid crystals are composite functional materials having a variety of application ranging from display to smart window. These materials consist of liquid crystal in which micron size droplets of polymer is dispersed. In the present study the effect of different concentration of polymer 2-ethyl hexyl acrylate on optical and electrical properties of nematic liquid crystal 4-cynophenyl 4-n-hexyl benzoate were investigated by various techniques. The investigation of textures at different temperatures was performed by polarizing optical microscopy for the determination of phase transition temperature. The fabry perot scattering studies using low powered laser beam was used for the confirmation of phase transition temperature. Various textures were found according to the orientation of liquid crystal and polymer. The optical and electrical properties of pure liquid crystal were found to enhance after dispersing polymer. Our investigation suggest that after dispersing polymer into nematic liquid crystal, the material shows more stability, less flicking and sticking of image for display applications.
... To investigate the effect of micro-louver size on the viewing angle controllable ability, four micro-louver structures with the same thickness are fabricated by utilizing thiol-ene photopolymerization (40-40 µm, 40-60 µm, 60-40 µm and 60-60 µm) (Figure 3c-f), four controllable anti-peeping devices can realize WVA and NVA modes at 0 and 8 V [33]. However, external switchable anti-peeping films need to be installed on the screen, to solve this problem, the LCD containing the switchable antipeeping film is fabricated based on PDLC, the propagation direction of the light passing the 3M light control film can be tuned by the PDLC film, the NVA mode is presented without electric field and WVA mode is shown in the application of electric field (24 V) [34]. Crystals 2022, 12, x FOR PEER REVIEW 6 of 11 ...
As we move from the industrial age to the information age, nowadays, the opportunity to access personal information in public increases as personal computers (PCs), cell phones, automated teller machines (ATM) and other portable display devices have come into wider use, so it is well suited for these liquid crystal displays (LCDs) to switch between wide viewing angle (WVA) (share mode) and narrow viewing angle (NVA) (privacy mode). In this review, we have summarized structures, principles and characteristics of several devices that show great potential application in controllable anti-peeping displays in the eyesight of materials consist of pure liquid crystals (LCs), polymer dispersed LCs (PDLCs), polymer stabilized LCs (PSLCs) or polymer network LCs (PNLCs) and non-LCs, which provides systematic information for next-generation viewing angle-controllable LCDs with lower operating voltage, higher transmittance and good viewing angle controllable characteristics. Because LCs/polymer composite films have the advantages of long life, low power consumption and energy saving, they are regarded as the mainstream technology of next-generation viewing angle controllable displays.
... PDLC films can present a magic performance in that the films show an opaque state in the absence of an electric field and exhibit a transparent state on the application of an electric field with sufficient strength [8,9]. Owing to the magic electrically switchable light-transmittance performance, PDLC films have been commercialized and applied in smart windows [10], flexible large-area displays [11], projection systems [12], bioapplications [13,14], and other devices [15,16]. However, some major drawbacks still limit the application of PDLC products in some scenarios [17]. ...
In this work, two silicon nanostructures were doped into polymer/nematic liquid crystal composites to regulate the electric-optical performance. Commercial SiO2 nanoparticles and synthesized thiol polyhedral oligomeric silsesquioxane (POSS-SH) were chosen as the dopants to afford the silicon nanostructures. SiO2 nanoparticles were physically dispersed in the composites and the nanostructure from POSS-SH was implanted into the polymer matrix of the composites via photoinduced thiol-ene crosslinking. SEM results indicated that the implantation of POSS microstructure into the polymer matrix was conducive to obtaining the uniform porous polymer microstructures in the composites while the introduction of SiO2 nanoparticles led to the loose and heterogeneous polymer morphologies. The electric-optical performance test results also demonstrated that the electric-optical performance regulation effect of POSS microstructure was more obvious than that of SiO2 nanoparticles. The driving voltage was reduced by almost 80% if the concentration of POSS-SH in the composite was nearly 8 wt% and the sample could be completely driven by the electric field whose voltage was lower than the safe voltage for continuous contact (24 V). This work could provide a creative approach for the regulation of electric-optical performance for polymer/nematic liquid crystal composites and the fabrication of low voltage-driven PDLC films for smart windows.
In this paper, we demonstrate the first ever dual-period diffraction gratings that do not require electrical tuning to obtain the effect of period change. Our method allows for multiplication of the base period by proper modification of the subsequent slits of the grating. The proposed elements are fabricated by selective photopolymerization of a composite based on a nematic liquid crystal. The gratings are formed by polymer stabilization of a liquid crystal in different orientations of the molecules in selected grating slits to allow for period manipulation. The operating principle is based on changing the phase delay introduced by the slits depending on polarization direction of incident light with respect to the director in each type of slit, which allows to change the grating’s period. The proposed technique was successfully utilized to obtain diffraction gratings with either doubling or tripling of the period.
Due to the discoloration properties under different applied voltages, dye-doped polymer-dispersed liquid crystal (PDLC) films are widely used as camouflage nets and invisibility cloaks. However, the range of the discoloration has an intuitive effect on their applications. In this work, we studied the gamut range of PDLC film doped with dyes of red, green, blue, and yellow, with the concentration corresponding to the minimum haze of these dyes. The influence of the applied voltage on the color range of single-layer and double-layer films with different backgrounds was studied. The relationship of the voltage with the color was set from 0 V to 60 V at steps of 5 V, to characterize the discoloration of the PDLC films. The results showed that the films could cover 42.48% of the sRGB gamut and even exceed the range.
In this work, we provide a fabrication method for dual-responsive electrochromic (EC) polymer dispersed liquid crystal (PDLC) devices. The EC PDLC device was developed by combing the PDLC technique and a colored complex formed via a redox reaction without a specific EC molecule in a simple preparation method. The mesogen played dual roles in the device for scattering in the form of microdroplets and participating in the redox reactions. Orthogonal experiments were performed with the acrylate monomer concentration, the ionic salt concentration, and the cell thickness as factors to investigate the electro-optical performance for the achievement of optimized fabrication conditions. The optimized device presented four switchable states modulated by external electric fields. The light transmittance of the device was changed by an alternative current (AC) electric field while the color change was realized by a direct current (DC) electric field. Variations of mesogen and ionic salt species can modulate the color and hue of devices, which solves the disadvantage of a single color for traditional EC devices. This work lays the foundation for realizing patterned multi-colored patterned displays and anti-counterfeiting via screen printing and inkjet printing techniques.
As many displays are installed inside electric vehicles, technologies for controlling the viewing angles are attraction. We demonstrate a viewing-angle controllable device comprising hybrid-aligned nematic (HAN) liquid crystals. In the narrow viewing mode, the optical axis distribution in the HAN cell changes from hybrid to twist by changing the viewing angle from normal to oblique. The proposed HAN cell can be switched to wide viewing mode by applying a vertical electric field. Therefore, the switchable viewing-angle-controllable device can control the driver's viewing angle and block the reflected light from the co-driver's window. The proposed mechanism can be further applied to construct an achromatic polarization rotator with angle-dependence.
When a pure liquid crystal is dispersed into a suitable polymer to form micron-sized droplet, then it is called Polymer-dispersed liquid crystal (PDLC). In the present study, PDLC of different concentrations were prepared by dispersing a conducting polymer poly (3, 4–ethylenedioxy thiophene): poly (styrene sulfonate) into a cholestryl palmitate. The differential scanning calorimetry and fabry perot scattering studies were employed to study thermal and optical properties. It was found that the phase transition for PDLC occurs at a temperature different than those exhibited by pure liquid crystal. The behaviour of PDLC for parallel and perpendicular electric field has been investigated and the dielectric constant is determined. The value of dielectric constant and conductivity were found to increase with increasing concentration of polymer. The bistability and reflective properties of pure cholesteric liquid crystal can be minimized by dispersing polymer which makes material suitable for high contrast at large viewing angles.
Polymer-dispersed liquid crystals (PDLCs), comprised of submicron-sized LC droplets embedded in a continuous polymer matrix, have been the subject of interest for scientists and manufacturers owing to their promise for optoelectronic applications. Recently, many research works have made significant progress in improving performance, developing new operation modes, and expanding the application fields for PDLCs. In this review, recent advancements in the research work for performance optimization, novel operation modes, and application developments of PDLCs are overviewed. The working principle and the general fabrication procedure of PDLCs with different modes are first briefly explored. Then, the recent research developments performed in the preparation, experimental investigation, and applications of PDLCs are summarized systematically. Eventually, the challenge and future improvement are also discussed.
The investigations of optical properties are one of the greatest fascinating and essential characteristics of liquid crystal for technological applications. We report the effect of various concentrations of conducting polymer on optical behavior of cholesteric/chiral nematic liquid crystal. The study of molecular structure was performed using fourier transform infrared spectroscopy. The morphology and phase transition temperature for various cycles of heating and cooling was investigated by polarizing optical microscopy with crossed polarizers. After dispersing the conducting polymer, the composite shows new phase transition in addition to the existing phase and the mesophase range was found to increase. The dependence of refractive index on temperature and wavelength was investigated by abbe’s refractometer. The refractive index was found to increase with increasing concentration of conducting polymer which may be useful for devices employing these materials.
In this paper, polymer-dispersed liquid crystal (PDLC) films were prepared from a blend of prepolymer, liquid crystal and BaTiO3 (BTO) nanoparticle-laden nanofibres films by a polymerisation-induced phase separation (PIPS) method. By contrasting the microstructure and electro-optical curves of various proportions of monomer types, it was demonstrated that the hole size of the polymer network had a significant influence on the electro-optical nature of the PDLC films. nanofibres films loaded with different BTO nanoparticle contents were introduced into the liquid crystal mixture specimens, and the alterations in the polymer network, electro-optical nature of these specimens were analysed using SEM images, EDS and electro-optical curves. The electro-optical nature of the nanofibres films doped with PDLCs were found to be improved and the ageing resistance was greatly enhanced. Therefore, the development of PDLC films with faster response times and better electro-optical nature of reticular nanofibres films doped with PDLCs will significantly improve the promising technological applications of PDLC-based equipment for optical windows, displays, energy storage and flexible devices.
The study presents a quantum mechanical (QM) analysis of terephthalylidene-bis-[4-n-decylaniline] (TBDA) liquid crystal molecule by the method of first principle. The mesomorphic studies are performed using a polarizing optical microscope, Structural characterization of the material is performed by IR spectroscopy, and geometry optimization, thermochemistry, atomic charge distribution, frontier orbital analysis, population analysis, total electron density mapping, and nonlinear optical analysis are performed in detail at DFT/B3LYP level of theory. The studies provide a clear understanding of molecular dynamics, charge dynamics, and nonlinear effects for TBDA.
In this study, a method to regulate the visible transmittance in off-state (Toff) and the contrast ratio (CR) for polymer-dispersed liquid crystals (PDLCs) via electrospinning polyvinyl alcohol (PVA) nanofibers on ITO surfaces in liquid crystal cells was reported. The PDLC samples were prepared in the conventional liquid crystal cells and in the nanofiber cells. The results indicated that the sample in the nanofiber cell presented a lower Toff and a larger CR in comparison with the sample in the conventional cell if the samples were prepared under the same UV light.
In this work, the effects of the preparation conditions on the electro-optical performance and the polymer morphology of the polymer dispersed liquid crystal (PDLC) samples in which the polymer matrix contained polyhedral oligomeric silsesquioxane (POSS) microstructure were studied. The results confirmed the dramatic improvement effect of POSS microstructure for the electro-optical properties of PDLC. Moreover, the electro-optical performance and the polymer morphology of the PDLC samples with POSS microstructure can be regulated successfully by the preparation conditions, such as UV light intensity and polymerization temperatures. This work can provide a way for regulating methods for PDLC films.
Polymer-dispersed liquid crystals (PDLCs) exhibiting transmittance switching are utilized for preserving energy and protecting privacy. Here we prepared a typical PDLC mixture from a commercially available polymer and liquid crystal with nano-beads. A wire-bar coater was used to coat the PDLC mixture on indium-tin-oxide-coated glass, and a PDLC cell was assembled by coupling another glass in a vacuum, instead of a polymer film. Uniform glass-based PDLCs were fabricated successfully with an area of 15 × 15 cm², while an injection process with capillary action was not available for this large-scale device fabrication. The switching behavior of the cells was characterized by ramping the AC voltage, and a transmittance change of ∼70% was measured. In a typical roll-to-roll process, only flexible polymer films have been used in lamination, in which deterioration in transparency occurs over the course of time, reducing the efficiency. In this study, to improve the optical properties, PDLC switchable glazing is fabricated directly onto glass substrates instead of onto plastic polymers. This PDLC switchable glazing, exhibiting low haziness and wide-angle vision, can be fabricated at a large scale by a vacuum-coupling process, with potential use as glass windows for energy-efficient buildings.
Optical diffusers with high transmission, high haze and excellent diffusing ability are widely needed in backlight unit (BLU) of liquid crystal displays (LCDs). However, there are still drawbacks in the particles-doped optical diffusers, including the distribution of the scattered particles due to agglomeration of particles and complex coating process. In this paper, polymer/liquid crystal (LC) composite films which are based on the epoxy resins, polyamine (PA) and varied thiol monomers were firstly prepared by thermally initiated polymerisation. The morphologies and optical properties of the composite films were systematically investigated. By controlling the functionality of thiol in the system of epoxy resins/thiol/PA/LCs, as the light scattering of anisotropic LCs and isotropic polymer framework is both achieved in the optical diffusers, good diffusing ability and high visible transmission (total transmission >96.0% and transmission haze > 95.0%) are obtained.
A new class of smart window technologies are gaining interest as they have the functionality to control dynamic solar radiation, shading, ventilation and energy production. They are capable of improving buildings’ energy performance by adapting to different climate conditions and bring thermal and visual comfort for occupants. Polymer-dispersed liquid crystal (PDLC) is a smart switchable window that changes its optical transmissions from translucent to transparent when an alternating electric current stimulus is introduced. The present paper discusses the results of an indoor investigation for the optical and thermal performance of a PDLC glazing system. The spectral transmittance of the investigated PDLC was evaluated for both the translucent and transparent states using UV–vis–NIR (1050) spectrophotometer. In addition, the thermal investigation was carried out in an indoor condition utilising a test cell equipped with a small scale of PDLC glazing, which was exposed to (1000, 800, 600, 400 W/m²) solar radiation for 180 min. The optical evaluation showed that the investigated PDLC glazing offered low transmission for UV (8%) and NIR (44%) in the translucent state, respectively. The result of SHGC was 0.68 and 0.63 for the transparent and translucent states, respectively, which indicates that the investigated sample could be more effective in reducing heat loads in a cold dominated climate. The U-value for the PDLC glazing was 2.79 W/m² for the transparent and 2.44 W/m² translucent.
Display devices with the narrow viewing angle (NVA) and the wide viewing angle (WVA) characteristics can simultaneously meet the demands for privacy protection and information sharing. Herein, we propose a novel method for fabricating a controllable anti-peeping device with a laminated structure of microlouver and polymer dispersed liquid crystals (PDLCs) film, and this device can be reversibly switched between a wider viewing angle range (VAR) for the WVA mode and a narrower viewing angle range (VAR) for the NVA mode at 0 V and 8 V, respectively. Also, the VARs of the controllable anti-peeping device can be dynamically tuned by varying dimensions of the microlouver structures and applying various voltages across the PDLCs film from 0 V to 8 V. The as-fabricated device provides display devices with controllable viewing angle characteristics, which can be applied in the display field with fascinating and practical functions.
Liquid crystals displays (LCDs) currently dominate the display market, wherein a wide viewing angle is considered as one of the most important characteristics. However, for LCDs with wide viewing angles, some private information inevitably becomes more visible; thus, an LCD with a switchable viewing angle has attracted greater interest. Here, we report a novel switchable viewing angle film that can make the viewing angle of an LCD electrically switchable between ±30° and ±60°, i.e. between an anti-peeping mode and a share mode, by 5.0 V is turned on and off, respectively. The response time necessary to change between the modes is in milliseconds. It is believed that it has potential applications in LCDs with high quality.
A novel light diffuser based on a thermally cured polymer dispersed liquid crystal (PDLC) film was facilely fabricated by the thermal curing of epoxy monomers with thiols and polyamine (PA) in a composite solution of monomers and liquid crystals (LCs) sandwiched by two clean polyethylene terephthalate (PET) substrates. Varied amounts of LCs, diluent effects of epoxy resins and thiols and different curing temperatures have been investigated in the preparation of the films, and the optical properties (total transmittance and transmittance haze) and the light diffusing abilities of these films were also studied. As the microstructures of the polymers in the films were analysed using light scattering theory, it was revealed that the total transmittance of the novel light diffuser, with a combined polymer morphology of polymer networks and polymer balls, can reach 93% by simultaneously possessing a high transmittance haze (95%). The novel light diffuser, based on thermally cured PDLCs, possesses a good diffusion capacity and will have promising potential applications in military projects and liquid crystal display (LCDs) devices.
Polymer-dispersed liquid crystals (PDLCs), composed of micro-sized liquid crystal domains embedded in a continuous polymer matrix, are an important class of materials that hold promise for many opto-electronic applications. In this review, based on an analysis of research publications appearing between 2006 and 2012, preparation of conventional PDLCs and nanoparticles-doped PDLCs, their properties, and their application for opto-electronic devices are described.
Multiview three-dimensional (3D) displays can project the correct perspectives of a 3D image in many spatial directions simultaneously. They provide a 3D stereoscopic experience to many viewers at the same time with full motion parallax and do not require special glasses or eye tracking. None of the leading multiview 3D solutions is particularly well suited to mobile devices (watches, mobile phones or tablets), which require the combination of a thin, portable form factor, a high spatial resolution and a wide full-parallax view zone (for short viewing distance from potentially steep angles). Here we introduce a multi-directional diffractive backlight technology that permits the rendering of high-resolution, full-parallax 3D images in a very wide view zone (up to 180 degrees in principle) at an observation distance of up to a metre. The key to our design is a guided-wave illumination technique based on light-emitting diodes that produces wide-angle multiview images in colour from a thin planar transparent lightguide. Pixels associated with different views or colours are spatially multiplexed and can be independently addressed and modulated at video rate using an external shutter plane. To illustrate the capabilities of this technology, we use simple ink masks or a high-resolution commercial liquid-crystal display unit to demonstrate passive and active (30 frames per second) modulation of a 64-view backlight, producing 3D images with a spatial resolution of 88 pixels per inch and full-motion parallax in an unprecedented view zone of 90 degrees. We also present several transparent hand-held prototypes showing animated sequences of up to six different 200-view images at a resolution of 127 pixels per inch.
An optically isotropic liquid crystal (LC) such as a blue phase LC or an optically isotropic nano-structured LC exhibits a very wide viewing angle because the induced birefringence is along the in-plane electric field. Utilizing such a material, we propose a liquid crystal display (LCD) whose viewing angle can be switched from wide view to narrow view using only one panel. In the device, each pixel is divided into two parts: a major pixel and a sub-pixel. The main pixels display the images while the sub-pixels control the viewing angle. In the main pixels, birefringence is induced by horizontal electric fields through inter-digital electrodes leading to a wide viewing angle, while in the sub-pixels, birefringence is induced by the vertical electric field so that phase retardation occurs only at oblique angles. As a result, the dark state (or contrast ratio) of the entire pixel can be controlled by the voltage of the sub-pixels. Such a switchable viewing angle LCD is attractive for protecting personal privacy.
This study examined the viewing angle control of twisted nematic liquid crystal displays (TN-LCDs). Conventional TN mode has intrinsic characteristics, such as a narrow viewing angle along the vertical direction and a relatively wide viewing angle along the horizontal and diagonal directions. Our study shows that the viewing angle of the TN-LCD can be made wider and smaller than that of a normal TN cell by adding one or two homogeneously aligned liquid crystal layers between the TN cell and polarizers, and controlling their retardation with an applied voltage.
We demonstrate a controllable viewing angle liquid crystal display (LCD) using an inserted blue-phase liquid crystal (BPLC) cell. The BPLC layer functions as a tunable positive C-film or a negative C-film, depending on whether the employed LC has a positive or negative dielectric anisotropy. Therefore, the viewing angle of the LCD panel can be controlled continuously by the applied voltage of the BPLC cell.
The fluorescence enhancement of QDs-doped TiO2/polymer, LCs/polymer, and TiO2/LCs/polymer composite systems was comparatively studied. It was proposed that the large photoluminescence enhancement of QDs was induced by the synergistic effect of LCs/polymer composite and TiO2 nanoparticles possessing 150 nm particle size and 0.1 wt% loading content. The enhancement factor of QDs-doped TiO2/LCs/polymer nanocomposite film was approximately 6-fold relative to the QDs-doped polymer. Moreover, this nanocomposite film enabled to realise electrically tuning of photoluminescence intensity and be prepared by a facile UV polymerisation and large-scale manner. Furthermore, the excellent mechanical properties nearly remained unchanged doping 0.1 wt% TiO2 in this LCs/polymer composite.
In this paper, by utilising the photoinitiated cationic polymerisation of liquid crystalline epoxide in LC solvents, the epoxy-based polymer stabilised liquid crystals (EPSLCs) were fabricated. The effects of the liquid crystalline epoxide content, UV intensity, polymerisation temperature, and initiator content on the network morphology of liquid crystalline epoxy polymers (LCEPs) and electro-optical characterisations of EPSLC samples were studied. The results suggested that the preparation conditions had a dominant effect on the morphology of the LCEP and the void size in the EPSLC sample. The increase of liquid crystalline epoxide content, UV intensity, and initiator content induced that the density of LCEP network became larger and the void size decreased, which resulted in that the stabilising effect from the LCEP network on the mesogenic solvent molecules was strengthened. Conversely, the increase of polymerisation temperature induced that the stabilising effect from the LCEP network on the LC molecules was weakened.
As a typical class of electrically light-transmittance-switchable (ELTS) composites materials, polymer dispersed liquid crystal (PDLC) films have been widely used in displays, smart windows, light shutters, etc. However, the commercialised PDLC film still requires a comparatively high voltage to maintain its transparent state, leading to huge power consumption and even a potential safety risk. In this regard, we proposed a ‘heat followed UV’ stepwise polymerisation strategy for preparing a kind of ELTS film with a low driving voltage (~20.7 V) through constructing a coexistent system of polymer dispersed and polymer stabilised liquid crystal (PD&SLC). In this new PD&SLC system, vertically orientated polymer networks were formed within LC domains to induce the vertical alignment of LC, thereby reducing the driving voltage. Also, the as-made PD&SLC film exhibited good flexibility due to the high content of polymer. Moreover, the effects of the liquid crystalline polymerisable monomers content on the polymer morphologies as well as the electro-optical properties of the as-made PD&SLC films were elaborately investigated.
In this paper, polymer dispersed liquid crystal (PDLC) films based on epoxy-mercaptan system were prepared by thermal-initiated polymerization. The effects of the liquid crystal (LC) content, the proportion and the functionality of epoxy monomers on the polymer structures and electro-optical properties of the as-made PDLC films were investigated systematically. It was found that the morphologies of the polymer matrix can be altered from polymer meshes to polymer balls by increasing the LC content as well as the functionality of epoxy monomers. Accordingly, the electro-optical properties could be regulated by the morphologies of polymer networks. Especially, the as-made PDLC films with homogeneous porous structures exhibited the optimal electro-optical properties. Consequently, this work offers a meaningful approach to control the microstructures and optimize the electro-optical properties of PDLC films, which indeed can form a wonderful footstone for the wide application of PDLC.
A novel approach to fabricate epoxy-based polymer-stabilized liquid crystals (EPSLCs) via the cationic photopolymerization of liquid crystalline epoxide in mesogenic solvents was presented. The photoinitiated cationic polymerization of liquid crystalline epoxide in different mesogenic solvents was compared and the liquid crystalline epoxy polymer (LCEP) network can only be formed in the particular solvents. The different photo-curing behaviors of the liquid crystalline epoxide in various solvents may be ascribed to the solvent effect and the content of the nucleophilic groups had a decisive influence on the formation of the LCEP network. The epoxy polymer/liquid crystal (LC) composites were also prepared by the cationic photopolymerization of different epoxy monomers in LC solvent. The morphology of the epoxy polymers in the composites and the change of the arrangement of LC molecules before and after polymerization were also studied. Moreover, the stabilizing effect of the LCEP network on the LC molecules was also characterized by the electric-optical performance test. This report can offer an innovative technique to fabricate EPSLCs and provide a promising means for the development of functional epoxy polymer composites.
A liquid crystalline epoxide was synthesized and its curing reactivity was compared with that of the conventional epoxy monomers. By utilizing the difference in curing reactivity between the liquid crystalline epoxide and non-liquid crystalline epoxy monomers, a coexistent system of polymer-dispersed and polymer-stabilized liquid crystal (LC) in the intelligent films can be obtained by two-step thermal curing method. If the later curing process was undertaken under an external electric field, the ordered microstructure of liquid crystalline epoxy polymer (LCEP) network can be implanted into the conventional epoxy resin. The competition of the anchoring effect on the LC molecules from the LCEP network and the conventional epoxy resin matrix was crucial to the electro-optical performance of the films. Moreover, the performance of the films can be adjusted by controlling the content of liquid crystalline epoxide and the external electric field applied during later curing. This approach can provide a facile route to regulate the electric-optical performance of polymer-dispersed liquid crystal films for practical applications.
In this paper, we report the design, preparation and properties of epoxy-mercaptan polymer/nematic liquid crystal (LC) composites with electrically switchable optical transmittance. It is found that the polymer microstructure can be regulated from porous structure to microspheres or beads by appropriately modulating the curing temperature, the molecular structure of mercaptan, as well as the compositions of epoxy, mercaptan and nematic LC host. Under an external electric field, the thin films based on such composites can switch from opaque to transparent. The electro-optical performance is found to be highly dependent on the polymer microstructures and the optimum characteristics can be achieved in the composite with a microstructure of smaller microspheres. The possible mechanism for the formation of polymer microspheres and the effects of the microstructures on the electro-optical characteristics of the composites are also discussed. This work is expected to provide an efficient way to control the microstructure of epoxy/mercaptan polymer and develop the composites with switchable optical transmittances for both civil and military applications.
Polymer-dispersed liquid crystal (PDLC) films have been successfully applied in the field of smart windows, building partitions and projection screens. However, the high-driving voltage of the state-of-the-art PDLC films not only results in serious security problems but also leads to huge energy consumptions. Although studied for decades, however, no tangible improvements of reducing the driving voltage have been achieved due to the movements liquid crystals (LCs) are greatly confined by the porous polymer structures of PDLCs. In this paper, an electrically light-transmittance-controllable film with an unprecedented low-driving voltage (more than 50% lower than that of the typical PDLC films) was prepared from a new polymer dispersed and stabilised cholesteric LC system. Also, the effects of the amounts of chiral dopants on the electro-optical properties were studied.
Light scattering by an optically anisotropic liquid crystal (LC) droplet of a nematic in an isotropic polymer matrix is considered in the Wentzel–Kramers–Brillouin (WKB) approximation. General relations are obtained for elements of the amplitude matrix of light scattering by a droplet of arbitrary shape and for the structure of the director field. Analytic expressions for the amplitude matrices are derived for spherical LC droplets with a uniformly oriented structure of local optical axes for strictly forward and strictly backward scattering. The efficiency factors of extinction and backward scattering for a spherical nonabsorbing LC droplet depending on the LC optical anisotropy, refractive index of the polymer, illumination conditions, and orientation of the optical axis of the droplet are analyzed. Verification of the obtained solutions has been performed.
A viewing angle controllable fringe and in-plane switching vertical alignment liquid crystal display (LCD) structure has been proposed. To realise the change from wide viewing angle (WVA) to narrow viewing angle (NVA) in a single LCD panel, the bias voltage is applied on the common electrode, and NVA can decreases with the increasing bias voltage. In WVA mode, the viewing angle cone (contrast ratio larger than 1000:1) is almost 70° and the contrast ratio is larger than 100:1 in arbitrary azimuthal directions. In NVA mode, the viewing angle cone (10:1) can continuously and uniformly change from 40° to 20°.
We propose a viewing angle switchable blue-phase liquid crystal display with low voltage and high transmittance. In this device, in-plane protrusions are used to lower operating voltage and improve the transmittance. Besides, the top electrode can control viewing angle of the proposed display. When no voltage is applied to the top electrode, the display shows wide viewing angle mode. On the contrary, this display shows narrow viewing angle mode. So, this device exhibits low operating voltage, high transmittance, and good viewing angle controllable characteristics.
This paper discusses modern principles of constructing displays based on liquid crystals, which provide high-contrast images at large viewing angles. The characteristics of displays based on the twist and supertwist effects and the transverse electric-field effect are considered, along with optical compensator films and multidomain vertically oriented structures. Displays with controllable field-of-view angles are described.
A device for operating viewing angle-switchable liquid crystal displays has been developed based on an optically isotropic liquid crystal (OILC). The device comprises two panels, main and switching. Depending upon the voltage applied, the optical state of the OILC layer in the switching panel can be changed to the anisotropic uniaxial state, taking on the role of a positive C film. In this manner luminance at oblique polar angles can be suppressed, resulting in a dark image at an off-normal axis, at the same time retaining good image quality in the normal direction. Depending on the switching of the OILC layer, wide or narrow angles of viewing can be obtained.
We demonstrated a novel viewing angle controllable display device in in-plane switching (IPS) mode with single panel. In the device, single pixel is separated into two regions, named as main pixel for displaying images and sub pixel for viewing angle control. Initially, the liquid crystal (LC) in sub pixel is homogenously aligned on substrate. For wide viewing angle mode, the LC switches in plane in the main pixel and for narrow viewing angle mode the LC switches the level of tilt angle without rotating by applying fringe electric fieldge. The proposed device is facilitated with simple manufacturing process and good viewing angle control with single panel.
New optoelectronic materials based on polymer dispersed liquid crystals (PDLC) show great potential for application in displays, temperature sensors, optical computing and for solar energy control. We report liquid crystal, termoset or thermoplastic materials. PDLC materials may be formed by several different processes. The liquid crystal may be dissolved in low molecular weight polymer precursors, in a thermoplastic melt or with a thermoplastic in a common solvent. Subsequent polymerization, cooling of the polymer melt or solvent evaporation lead to liquid crystal immiscibility, droplet formation and growth, and polymer gelation. The optoelectronic properties of these materials are affected by the droplet morphology. Specific examples are presented for each of these processes and it is demonstrated how the droplet morphology and density, and thus device performance, can be controlled by each method. The thermoplestics are suitable for forming films by a variety of techniques. A range of polymers and liquid crystals may be used to form PDLC materials, allowing them to be tailored for any of a number of applications.
Viewing angle switching from a wide viewing angle to a narrow viewing angle has been studied. Conventional multidomain vertical alignment (VA) mode offers the advantages of a high contrast ratio (CR) not only in the front view but also in the wide viewing directions only if compensation films such as a negative C plate and a positive A plate are used. The positive A plate can be replaced by a homogeneous aligned (HA) liquid crystal layer, and the retardation of the HA layer at the off axis can be controlled by applying an electric field while keeping the retardation value at zero in the normal direction. Consequently, the viewing angle range of a VA device can be controlled from a wide viewing mode (over 170° in terms of CR = 10) to a narrow viewing angle mode (approximately 60° in terms of CR = 2) in the horizontal direction while keeping a high image quality at the normal direction.
THE leading technology for flat, high-resolution computer and television screens is based on twisted nematic liquid-crystal displays1. The successful operation of these displays requires control of molecular alignment, which is currently achieved by confining the liquid crystal between mechanically rubbed surfaces2. But in addition to the practical difficulties associated with rubbing, the resulting displays suffer from restricted viewing angles arising from the uniaxial nature of the alignment process3,4. This latter problem can in principle be circumvented if molecular alignment is varied, in a controlled manner, within individual pixels5–9. Exposure of functionalized substrates to polarized light offers a means of achieving high-resolution patterns in the plane of the display10–12. But to ensure that the alignment pattern imposed on the liquid crystal is free of orientation defects, the tilt angle between the long molecular axes and the substrates must be precisely controlled13,14. Here we show how our earlier linear photoalignment strategy10,12 can be extended to obtain such control, and thereby fabricate stable, multi-domain pixel displays with markedly improved fields of view.
A study was conducted to introduce chirality to a liquid crystal (LC) system through hydrogen (H)-bond self-assembly between a chiral donor (S)-2-fluoro-4-(2-octyloxy) benzoic acid (SFBA) and a 4-(4-trans- propylcyclohexyl)phenyl isonicotinate (PPI) achiral acceptor. The hydrogen-bonded LC complexes from SFBA and PPI showed blue phase (BP) in a broader temperature and concentration region. The H-bonded complexes were prepared by mixing of the precursors in appropriate proportions in a nonprotic solvent and by slow evaporation. These complexes in different molar ratios were found to exhibit several mesophases without the chiral acids and PPI exhibiting any mesophases. This process indicated the creation of a new mesogenic unit through H-bonding between PPI and the acids. The stability of the H bond in the complexes of SFBA and PPI was directly confirmed from temperature-dependent IR spectra.
The electro‐optic response of polymer dispersed liquid‐crystal (PDLC) films is reported as a function of frequency and amplitude of the applied voltage and size of the LC droplets. We found that the threshold voltage is minimum and sharpest at frequencies near a few kHz. Visual and optical response studies show that there are two types of PDLC films; type I, which exhibit large partial optical memory, and type II, which quickly regain their original levels of transmittance after switching off relatively small driving voltage. It was observed that both types of PDLC films, in general, exhibit a two‐step decay involving fast and slow components. However, the order in which the two components appear as the voltage is increased is different for the two types of PDLC films. Observations under the polarizing microscope show that the LC droplets in the two types of PDLC films undergo different transformations as the applied voltage is changed.
The light scattering and electro‐optic response of new material with display potential are investigated. The materials consist of microdroplets of nematic liquid crystals which are spontaneously formed in a solid polymer at the time of its polymerization. Droplet size, spacing, and distribution are readily controlled in these materials to allow optimization of displays based upon electrically controlled light scattering from the liquid crystal droplets. Preliminary experimental and theoretical studies of the light scattering properties show these materials to offer new features suitable for many display applications.
All conventional viewing angle switchable liquid crystal displays with pixel division have drawback in light efficiency because the sub-pixel that controls viewing angle does not transmit the incident light at normal direction. In this paper, we propose new viewing angle controllable homogeneously aligned liquid crystal display in which the pixel is composed of red, green, blue, and white pixels. The colored pixels are driven by fringe-field switching and the white pixel is driven by complex field. In wide-viewing angle mode, the liquid crystal (LC) directors in all pixels rotate in plane, contributing to high transmittance. In narrow-viewing angle mode, the LC directors in color pixels rotate in plane for light transmission while the LC directors in white pixel can rotate or tilt upward by simultaneous fringe and vertical electric field. The high tilted LC directors generate light leakage in oblique directions which can be utilized for viewing angle control and also transmission at normal direction for image expression. The proposed device overcomes the long standing problem of transmittance sacrifice in the conventional devices.
A chiral nematic liquid crystal/chiral ionic liquid composite with unique electro-optical characteristics is reported. The composite can be switched electrically between three different light states: transparent, scattering, and mirror reflecting (see images). Moreover, the reflection bandwidth can be controlled accurately and reversibly by adjusting the intensity of the electric field applied.
The scattering matrix, differential cross section, and the total cross
section for a small nematic droplet are derived in the Rayleigh-Gans
approximation. Different nematic director configurations are considered
for the droplet. Those studied are the configurations which result in a
spherical droplet from different molecular anchoring angles at the
droplet wall. Configurations both in the absence and presence of an
applied field are derived and their scattering properties are examined.
Some simple cases are treated in detail and the results presented in
closed form. In other more practical cases numerical results are
presented for the differential and total cross section. Strong
dependencies on the impact and scattering angles are found. The
possibilities of determining droplet size and nematic director structure
from experimental light scattering data are discussed, as well as
features relevant to electro-optic light shutters.