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This study examined the impact of different concentrations of carbon nanotubes (CNTs) on five nematic hybrid liquid crystals (LCs) based on 5CB. Electro-optical properties of the composite were tested, and the interaction between CNTs and LCs was theoretically analysed by first principles. Experimental results showed the effect of CNTs on electro-optical properties of hybrid LCs depended on the groups contained in monomer LCs. LCs with polar groups at the end increased the dielectric anisotropy of the composite, while the impact of CNTs on hybrid LCs containing non-polar terminal monomers was the opposite. The same variation was reflected in splay elastic constants and clearing points. Meanwhile, dielectric anisotropy, splay elastic constant, and rotational viscosity coefficients all changed with CNTs doping concentrations, reflecting the order of binding stability between representative groups and CNTs, and the variation of threshold voltage and response time reflected the order of binding stability between LC molecules and CNTs, consistent with theoretical calculations. Conductivity tests showed the additive of CNTs increased the conductivity of the composite and revealed the impact of CNTs on threshold voltage. Dielectric tests showed the incorporation of CNTs increased dielectric real and imaginary parts in low-frequency regions and increased relaxation frequency in high-frequency regions. [ABSTRACT FROM AUTHOR]

Based on the traditional structure of in plane switching liquid crystal display, a cylindrical liquid crystal micro-lens array driven by interdigital electrodes is proposed, and its performance is studied. Firstly, the director distribution and relative phase difference distribution of liquid crystal molecules were calculated, which shows that this structure can be used to fabricate cylindrical liquid crystal micro-lens. Then, by comparing lenses of difference sizes, it is found that narrow electrodes should be selected for lens production, and the centre of the electrode gap should be selected as the central axis of a single liquid crystal micro-lens. Finally, a certain electrode structure is selected to explore its focal length, focusing quality and zoom time. The results show that the focal length of the liquid crystal micro-lens decreases gradually with the increase of the driving voltage. When the driving voltage is between 3 Vrms and 5.5 Vrms, the liquid crystal micro-lens has good focusing quality, and its corresponding focal length changes from 1.63 mm to 20.28 mm. Based on this structure, when the liquid crystal lens is driven by the above two voltages alternately, the time required for liquid crystal molecules to reach stability is 2.35 s and 3.87 s respectively. [ABSTRACT FROM AUTHOR]

Temperature measurement and control has an extremely important role in both scientific research and manufacturing. Capacitive liquid crystal (LC) temperature sensors can monitor the temperature using the linear variation of the capacitance of LC cell with temperature, but the sensitivity and other properties need to be improved. In order to improve the performance of capacitive LC temperature sensor, we propose to mix twisted nematic LC (1M10600-100) with ferromagnetic nanoparticles γ-Fe2O3 to prepare LC temperature sensor in this paper. The relationship between the capacitance change rate of different concentrations of nano-doped LC materials at 0.1–20 V and different temperatures was tested, the sensitivity of the sensor was calculated, and the mechanism of the effect of doped nanoparticles on the performance of the device was analyzed. The experimental results show that the sensitivity of the capacitive temperature sensor made of nano-doped LC with the concentration of 0.03 wt% is as high as 9.5 pF/°C at 12 V, which is about 14.87% higher than the undoped device, and its recovery and stability remain almost unchanged. The Pearson correlation coefficient only changes by 0.02%. The results of this paper provide some guidance for the improvement of the performance of capacitive LC temperature sensors, and the development of high-sensitivity temperature sensors based on LC materials. [ABSTRACT FROM AUTHOR]

In this paper, the microstructures of the dilute magnetic PDLC films, doped with low concentrations of γ-Fe2O3 nanoparticles, have hardly changed, but their electric-optical responses have distinctly changed. The experimental results show that the threshold voltage and hysteresis decreased with the increasing concentration of γ-Fe2O3 nanoparticles. Furthermore, at the relatively low concentration of γ-Fe2O3 nanoparticles (samples (0) and (1) according to ϕm of 0 and 0.11%), the reciprocity of the rise time increased nonlinearly with the increasing square of the applied voltage. However, at the relatively high concentration of γ-Fe2O3 nanoparticles (samples (2) according to ϕm = 0.15%), the reciprocity of the rise time increased linearly with the square of the applied voltage. Moreover, the reciprocity of the decay time was independent of the applied voltage and decreased with increasing the concentration of γ-Fe2O3 nanoparticles. These characteristics are due to the adsorption of free ions by γ-Fe2O3 nanoparticles. As a result, the interfacial interaction between liquid crystal droplets and the polymer matrix decreased, and the effective electric field inside the liquid crystal droplets increased. [ABSTRACT FROM AUTHOR]

The image sticking of the liquid crystal display (LCD) is related to the residual direct current voltage (RDCV) on the liquid crystal cell. The saturated residual DC voltage (SRDCV) can be obtained by analyzing the change of the capacitance of the liquid crystal cell under the application of DC bias (DCB), thus the LCD image sticking can be evaluated. Based on this, we evaluated the image sticking of the hybrid aligned nematic (HAN) liquid crystal display (HAN-LCD) with four different alignment layer materials (KPI-300B, PIA-2710, RV-961G, SE-4811(0526)) combinations of infused liquid crystal materials with negative dielectric anisotropy, from which the effect of the alignment layer material on image sticking was analyzed. The experiment found that the SRDCV measured by the HAN cell with vertical PI model SE-4811(0526) and parallel PI model PIA-2710 is the minimum under positive and negative DCB. The results show that the alignment layer material can greatly affect the image sticking problem of HAN-LCD, and provide useful guidance for improving its display quality. [ABSTRACT FROM AUTHOR]

In this paper, a highly sensitive and transparent flexible temperature sensor fabricated from the polyethylene terephthalate flexible substrate and the nematic liquid crystal (1M0921900-000) is proposed, which simultaneously has low power consumption. Using the relaxation time (τ = RC) as an intrinsic variable to characterise temperature, a better linear fitting with temperature can be obtained at low voltage, high precision and more stable temperature monitoring can be achieved. The maximum sensitivity is −4.05%/°C at 0.1 V and 200 Hz. The transmittance of the sensor can reach 62.36–81.13% in the visible light range. Compared with the rigid liquid crystal temperature sensor, the rise time and the decay time of the sensor are reduced by 97.104% and 90.313%, respectively. In addition, it also has good stability, recovery, and durability, which shows potential applicability to electronic skin, prostheses, robots, and biomedical by accurately monitoring the change of external temperature. [ABSTRACT FROM AUTHOR]

The polymer dispersed liquid crystal films doped with the low concentration γ-Fe2O3 nanoparticles coated with oleic acid were inverstigatited. The experimental results showed that the doped and un-doped polymer dispersed liquid crystal films were the similar surface morphologies, however their evolving curves of the capacitance with the applied voltage were different, as well as the transmission rate. The interpretations based on these differences were proposed, i.e. those came from the adsorbed free ions by the γ-Fe2O3 nanoparticles, instead of the electromagnetic properties of the γ-Fe2O3 nanoparticles. The effect of the free ions is equivalent to the negative dielectric constant and refractive index. Furthermore, the reduction of the free ion concentration due to the absorption in the doped polymer dispersed liquid crystal films can decrease the negative dielectric constant and refractive index, i.e. the effective dielectric constant and refractive index were increased. As a result, the contrast ratio increased significantly, and the driving and threshold voltages decreased distinctly. These results may be useful for electro-optics devices. [ABSTRACT FROM AUTHOR]

In order to explore the stability of a liquid crystal (LC) system doped with γ-Fe2O3 nanoparticles, the physical properties (clearing point, dielectric properties), electro-optical properties and residual direct-current voltage (RDCV) of the doped LC system were measured and evaluated at different times. First, the temperature was controlled by precision hot stage, and the clearing point temperature of doped LC was observed and measured by a polarized optical microscope. Using a precision LCR meter, we measured the capacitance-voltage curves of the doped LC system at the temperature of 27 °C. The dielectric constant of doped LC was calculated by the dualcell capacitance method. Then, the electro-optical properties of the doped LC system were measured. Finally, the RDCV of the doped LC system was measured and calculated. After five months, the parameters of the doped LC system were re-measured and analyzed under the same conditions to evaluate its stability. The experimental results show that, within five months, the clearing point change rate of doped LC is in the range of 0.24%–1.37%, the change of dielectric anisotropy is in the range of 0.035–0.2, the curves of electro-optical properties are basically fitted, and the change rate of saturated RDCV is about 11.2%, which basically indicate that the LC system doped with γ-Fe2O3 nanoparticles has good stability. [ABSTRACT FROM AUTHOR]

Temperature monitoring plays an increasingly important role in research and industrial applications. Based on the influence of liquid crystal material thermal sensitivity on the capacitance of liquid crystal cell, the sensing performance of the capacitive-type liquid crystal temperature sensor were studied. By testing the capacitance under the voltage from 0 V to 20 V at different temperatures, the capacitance–voltage curve is drawn, and then the relationship between the capacitance change rate and the temperature at different voltages was obtained, so as to analyse its sensitivity. The results show that the capacitance of the liquid crystal material (RDP-09 T-100) is linearly related to the temperature in the temperature range of 20–110°C, even when the applied voltage is 0.1 V, which proves its feasibility as a temperature measuring medium for the temperature sensor and shows that the sensor has the advantage of low power consumption. When the applied voltage is 15 V, the sensitivity of the capacitive-type liquid crystal temperature sensor can reach 0.94 pF/°C and its response time is 0.115 s/(pF.°C). This research further expands the application scope of liquid crystal and has certain guiding significance for the development of new temperature sensor. [ABSTRACT FROM AUTHOR]

In order to accurately determine the pre-tilt angle, we proposed a systematic method by combining optical and electrical measurement. First, the pre-tilt angles of the parallel and vertical aligned nematic liquid crystal (LC) cell with a large thickness (>10 μm) were measured by the crystal rotation method. Then, the material parameters of E7, including the dielectric constant and the splay and bend elastic constant, were obtained by using the dual-cell capacitance model and comparing the capacitance-voltage (C-U) curves of the thick cells. Finally, the pre-tilt angles of two thin LC cells to be tested were determined by theoretical and experimental fitting of their normalised C-U curve, which are 1.80°±0.04° and 3.50°±0.02°, respectively. Our method not only has relatively high accuracy, but also is not limited by the thickness and mode of LC cell. [ABSTRACT FROM AUTHOR]

The dynamic response property of liquid crystal (LC) devices mainly depends on the selection of LC materials and driving method of the devices. In this work, we explored the modulation of the dynamic response property of LC mixtures through the microscopic mechanism and macroscopic method of γ-Fe2O3 nanoparticle doping and driving mode adjustment, respectively. LC mixtures doped with different concentrations of γ-Fe2O3 nanoparticles retained the dielectric and elastic properties of the LC state and good temperature stability. In addition, doped LC mixtures had lower threshold voltage, higher birefringence, and faster rise and decay times than pure LC materials. Besides, the application of voltage overdriving and undershooting methods could reduce the rise and decay times of LC mixtures by 74.8% and 21.7%, respectively. Moreover, the combined methods of γ-Fe2O3 nanoparticle doping and voltage overdriving and undershooting decreased the total response time of LC mixtures by 71.5%, and the response speed of doped LC mixtures increased by 3-fold relative to that of the pure LC materials. [ABSTRACT FROM AUTHOR]

The dielectric and elastic properties of liquid crystals (LCs) generally depend on the molecule structure, such as polar group and carbon chain length. For further investigation of the influence of molecular structure on the dielectric and elastic properties of fluorine-containing tricyclic isothiocyanate LC, the experimental temperature was controlled at 25°C by precision hot stage, and a precision LCR meter was used to measure the capacitance of six LC cells under the voltage from 0.1 to 20 V at 1 kHz. An LC cell capacitance model and a dual-cell model were adopted to obtain the dielectric anisotropy, and the capacitance–voltage curves of six LC materials were plotted. The threshold voltage of Fréedericksz transition was analysed, and a finite difference iterative method was used to attain specific values of three elastic constants. The influence of molecular structure on the dielectric and elastic constants was finally analysed. Experimental results showed that the introduction of meta-difluoro group would increase the dielectric anisotropy and reduce the threshold voltage of LC. As the length of the alkyl carbon chain increased, the dielectric anisotropy would have an odd–even alternation effect, which would lead to changes in the elastic constants of LC. [ABSTRACT FROM AUTHOR]

In this study, the twist elastic constant (k22) of liquid crystals (LCs) was accurately measured using capacitance method. The constant can be obtained on the basis of accurate measurement of other LC parameters, such as parallel and vertical dielectric constants (ε// and ε⊥), splay and bend elastic constants (k11 and k33), and rotational viscosity coefficient (γ1). First, by using dual-cell capacitance method and an LC cell capacitance model to measure ε// and ε⊥, k11 and k33 can be obtained from the threshold voltage determined from the voltage-capacitance curve of the parallel-aligned nematic LC layer and the comparison between the experimental and theoretical results based on the Frank elastic theory, respectively. In addition, γ1 can be obtained from the measurement of the dynamic response in the parallel-aligned nematic cell. Finally, k22 can be accurately determined using the threshold voltage of the twisted nematic LC cell. By adopting the above method, the measured k22 for LC E7 was 6.7 × 10−12 N. The proposed method is more rigorous and yields a more accurate measurement result than the other methods reported in the literature. [ABSTRACT FROM AUTHOR]