Wide application of dichroic dye-doped liquid crystal device (DLCD) devices has been proposed, which removes conventional film-type polarizer in reflective LCD and OLED. Combination of DLCD, quarter-wave film and reflector can realize effective reflective LCD. In addition, by replacing conventional polarizer to switchable DLCD in OLED, the proper level of a low reflection is achieved, and more interestingly high brightness OLED can be realized if the optic axis of DLC is switched to vertical alignment when there is no ambient light, which could save power consumption and life time of OLED. Further DLCD can be applied to bi-functional device functioning as both smart mirror and light shutter.
Carbon nanotube (CNT), an extremely long hollow cylinder with nanometer-sized diameter, is a promising carbon material with unique thermal, electrical, and physical properties. Due to their peculiar and fascinating properties, CNTs have been studied and used in various industries since their discovery. The CNTs are potentially viable alternatives for conventional materials in electric devices considering their mechanical resilience, high electrical conductivity, and optical transparency. The alignment of CNTs into ordered structures garnered a special interest as it enhances electrical conductivity and optical transparency, and generates a new intriguing anisotropic optical absorption property. The optical properties of highly oriented CNT sheets have been investigated to apply as optical polarizer and polarized light source. Further, the flexible electrodes derived from an aligned CNTs have unveiled applications in super-capacitors, solar cell, and lithium-ion battery. Therefore, to utilize CNTs in LCD and many other flexible electronic device applications it is essential to attain highly ordered CNTs which should be static even under external stresses such as bending, pressing, and strain. In this work, we fabricated the aligned CNT sheet films (a-CSFs) in which the grown CNTs are stretched unidirectionally on the substrate and its orientation is fixed via polymerization of a coated monomer and then measured its optical and mechanical properties, testing feasibility of its application for multi-functioning films such as polarizer, electrode, and liquid crystal (LC) alignment. The fabricated a-CSF exhibits polarization efficiency (PE) (87.23% of 10 layers of a-CSF), sheet resistance (361.7 Ω/sq), and an excellent aligning capability of LC molecules as shown in Fig. 1 (a~c). Besides, flexibility and stability test of a-CSF via repeating bending test of 1,000 cycles at bending radius of 2 mm exhibited very low variation in the change ratio of sheet resistance and transmittance less than 8% and 10%, respectively. Utlilizing the mutifunctionalty of a-CSF, a liquid crystal display (LCD) with a twisted nematic(TN) mode was fabricated and exhibited feasibility of dynamic swicthing between bright and dark states on application of voltage off/on even without using conventional components of LCD such as transparent electrode, film-type polarizer, and polyimide-type alignment layer. We measured the voltage-dependent transmittance of both devices based on the a-CSF with 5 layers and 8 layers. The threshold voltage (Vth) and operating voltage (Vop) are defined as the voltage required to achieve 90% and 10% of transmittance relative to maximum transmittance, respectively. The measured Vth of both devices with 5 and 8 layers are 1.7 Vrms and 1.3 Vrms, respectively and the measured Vop of both devices are 7.6 Vrms and 4.3 Vrms, respectively. In the case of 8 layers, it shows slightly lower Vth and Vop, which is mainly due to the lower sheet resistance of a-CSF with 8 layers than 5 layers as shown Fig 2. In conclusion, we fabricated the multi-functional a-CSF with properties of the electrode, polarizer, and alignment layer based on the a-CSF using the simple fabrication process. We confirmed the a-CSFs exhibit better conductivity and PE in the visible regime. Furthermore, it has the excellent grooved morphology along the drawn direction of a-CS for homogeneous alignment of LC molecules. We carried out the bending test to confirm the stability of the films from mechanical stress. It showed excellent stability after bending tests of 1,000 cycles. The performance of the fabricated TN cells using a-CSFs were considerably working good. Figure 1
We propose an electrically tunable narrow bandwidth bandpass filter in which the band gap of polymer stabilized blue phase liquid crystal (PS-BPLC) with distinct crystallographic orientations can be tuned on electric field sweeps from red to blue with a narrow bandwidth (27 nm). Owing to the narrow bandwidth which can cut specific wavelength, it could be used as a filter to enhance color gamut in LCDs. In addition, the proposed bandpass filter exhibits much wider viewing angle property than Cholesteric LC bandpass filter.
Optically isotropic liquid crystal (OILC) composite film in which nano-sized LC droplets are embedded in a polymer matrix is highly useful for bendable displays and wearable photonics but a high operating voltage due to field shielding effect of the insulting matrix and low Kerr constant needs to be overcome. To address this challenge, a small amount of conductive materials PEDOT: PSS is doped into the OILCs. The LC cells with 2 and 3.5 wt% PEDOT: PSS doped OILCs exhibit improved driving voltages by 6.5% and 11.7% and on-state transmittance by 10.3% and 30.1%, respectively, compared to conventional one. In addition, faster switching response times are achieved while the dark level remains to be unaltered.
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