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. Graphical abstract

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. Graphical Abstract

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. Graphical abstract

Image sticking in thin film transistor-liquid crystal displays (TFT-LCD) is related to the dielectric property of liquid crystal (LC) material. Low threshold value TFT LC materials have a weak stability and the free ions in them will be increased because of their own decomposition. In this study, the property of TFT LC material MAT-09-1284 doped with γ-Fe₂O₃ nanoparticles was investigated. The capacitances of parallel-aligned nematic LC cells and vertically aligned nematic LC cells with different doping concentrations were measured at different temperatures and frequencies. The dielectric constants perpendicular and parallel to long axis of the LC molecules ε_⊥ and ε_//, as well as the dielectric anisotropy Δε, were obtained. The dynamic responses and the direct current threshold voltages in parallel-aligned nematic LC cells for different doping concentrations were also measured. Although the dielectric anisotropy Δε decreased gradually with increasing temperature and frequency at the certain frequency and temperature in LC state for each concentration, the doping concentration of γ-Fe₂O₃ nanoparticles less than or equal to 0.145 wt % should be selected for maintaining dynamic response and decreasing free ions. This study has some guiding significance for improving the image sticking in TFT-LCD.

Improving image sticking in liquid crystal display (LCD) has attracted tremendous interest because of its potential to enhance the quality of the display image. Here, we proposed a method to evaluate the residual direct current (DC) voltage by varying liquid crystal (LC) cell capacitance under the combined action of alternating current (AC) and DC signals. This method was then used to study the improvement of image sticking by doping γ-Fe₂O₃ nanoparticles into LC materials and adjusting the friction torque difference of the upper and lower substrates. Detailed analysis and comparison of residual characteristics for LC materials with different doping concentrations revealed that the LC material, added with 0.02 wt% γ-Fe₂O₃ nanoparticles, can absorb the majority of free ions stably, thereby reducing the residual DC voltage and extending the time to reach the saturated state. The physical properties of the LC materials were enhanced by the addition of a small amount of nanoparticles and the response time of doping 0.02 wt% γ-Fe₂O₃ nanoparticles was about 10% faster than that of pure LC. Furthermore, the lower absolute value of the friction torque difference between the upper and lower substrates contributed to the reduction of the residual DC voltage induced by ion adsorption in the LC cell under the same conditions. To promote the image quality of different display frames in the switching process, we added small amounts of the nanoparticles to the LC materials and controlled friction technology accurately to ensure the same torque. Both approaches were proven to be highly feasible.

The structures of flexodomains, which are similar to optical gratings and can be controlled by the amplitude of applied voltage and temperature, were verified through polarizing microscopy and light diffraction techniques. The properties of the optical grating induced by a bent-core nematic liquid crystal in planar cells with varied cell gaps and pretilt angles were studied. The period of optical grating decreases with the increase in the amplitude of the applied voltage and pretilt angle. In addition, the period increases with the increase in cell gap and temperature. The period of optical grating has a linear relationship with temperature. The continuously adjustable period has the potential to become an important and extended application of optical grating.