Fast-response liquid crystal lens with doping of organic N-benzyl-2-methyl-4-nitroaniline

Liquid crystal microlens array with positive and negative focal lengths based on a patterned electrode

A liquid crystal microlens array (LCMLA) with positive and negative focal lengths based on a ring-array patterned electrodes is demonstrated. By carefully designing patterned electrodes with a circular electrode array area and outer ring electrode region area, the switching of the positive and negative lens effect can be easily achieved in a single cell. A positive lens effect appeared when the voltage was applied to the outer ring electrode region and the top substrate. The focal length changed from infinity to 1 mm as the voltage varied from 0 to 3V_rms. A negative lens effect occurred when the voltage was applied to the circular electrode array and the top substrate. The focal length varied from infinity to -1mm when the voltage changed from 0 to 2V_rms. The imaging properties of the LCMLA at different voltages are evaluated. Our LCMLA, with simple structure, low driving voltage, and good stability, has potential applications in optical communication, imaging processing, and displays.

Superior improvement in dynamic response of liquid crystal lens using organic and inorganic nanocomposite

In this study, the response time of a 4 mm-aperture hole-patterned liquid crystal (HLC) lens has been significantly improved with doping of N-benzyl-2-methyl-4-nitroaniline (BNA) and rutile titanium dioxide nanoparticle (TiO₂ NP) nanocomposite. The proposed HLC lens provides the focus and defocus times that are 8.5× and 14× faster than the pristine HLC lens, respectively. Meanwhile, the focus and defocus times of the proposed HLC lens reach the order of millisecond. Result shows that the synergistic effect of BNA and TiO₂ NP induces a 78% decrement in the viscosity of pristine LC mixture that significantly shortens the focus and defocus times of HLC lens. The remarkable decrement in viscosity is mainly attributed to spontaneous polarization electric fields from the permanent dipole moments of the additives. Besides, the strengthened electric field surrounding TiO₂ NP assists in decreasing the focus time of HLC lens. The focus and defocus times of HLC lens are related to the wavefront (or phase profile) bending speed. The time-dependent phase profiles of the HLC lenses with various viscosities are calculated. This result shows the decrease in wavefront bending time is not simply proportional to viscosity decrement. Furthermore, the proposed HLC lens emerges a larger tunable focus capability within smaller voltage interval than the pristine HLC lens.

A Comparative Study on Electro-Optic Effects of Organic N-Benzyl-2-Methyl-4-Nitroaniline and Morpholinium 2-Chloro-4-Nitrobenzoate Doped in Nematic Liquid Crystals E7

Improvements in electro-optical responses of LC devices by doping organic N-benzyl-2-methyl-4-nitroaniline (BNA) and Morpholinium 2-chloro-4-nitrobenzoate (M2C4N) in nematic liquid crystals (LCs) have been reported in this study. BNA and M2C4N-doped LC cells have the fall time that is fivefold and threefold faster than the pristine LC cell, respectively. The superior performance in fall time of BNA-doped LC cell is attributed to the significant decrements in the rotational viscosity and threshold voltage by 44% and 25%, respectively, and a strong additional restoring force resulted from the spontaneous polarization electric field of BNA. On the other hand, the dielectric anisotropy (Δε) of LC mixture is increased by 16% and 6%, respectively, with M2C4N and BNA dopants. M2C4N dopant induces a large dielectric anisotropy, because the phenyl-amine/hydroxyl in M2C4N induces a strong intermolecular interaction with LCs. Furthermore, BNA dopant causes a strong absorbance near the wavelength of 400 nm that filters the blue light. The results indicate that M2C4N doping can be used to develop a high Δε of LC mixture, and BNA doping is appropriate to fabricate a fast response and blue-light filtering LC device. Density Functional Theory calculation also confirms that BNA and M2C4N increase the dipole moment, polarization anisotropy, and hence Δε of LC mixture.

Electro-optical effects of organic N-benzyl-2-methyl-4-nitroaniline dispersion in nematic liquid crystals

The dispersion of organic N-benzyl-2-methyl-4-nitroaniline (BNA) in nematic liquid crystals (LCs) is studied. BNA doping decreases the threshold voltage of cell because of the reduced splay elastic constant and increased dielectric anisotropy of the LC mixture. When operated in the high voltage difference condition, the BNA-doped LC cell has a fall time that is five times faster than that of the pure one because of the decrements in the threshold voltage of the cell and rotational viscosity of the LC mixture. The additional restoring force induced by the BNA’s spontaneous polarization electric field (SPEF) also assists to decrease the fall time of the LC cell. The decreased viscosity can be deduced from the decrements in phase transition temperature and associated order parameter of the LC mixture. Density functional theory calculation demonstrates that the BNA dopant strengthens the absorbance for blue light, enhances the molecular interaction energy and dipole moment, decreases the molecular energy gap, and thus increases the permittivity of the LC mixture. The calculation also shows that the increased dipole moment, polarizability, and polarizability anisotropy increase the dielectric anisotropy of the LC mixture, which agrees with the experimental results well. BNA doping has a promising application to the fields of LC devices and displays.

Liquid crystal lens with doping of rutile titanium dioxide nanoparticles

A 4 mm-aperture hole-patterned liquid crystal (LC) lens has been fabricated using a LC mixture, which consisted of rutile titanium dioxide (TiO₂) nanoparticles (NPs) and nematic LC E7, for the first time. The TiO₂ NP dopant improves the addressing and operation voltages of the LC lens significantly because it strengthens the electric field surrounding the TiO₂ NP and increases the capacitance of lens cell. Unlike the doping of common colloidal NPs, that of rutile TiO₂ NPs increases the phase transition temperature and birefringence of the LC mixture, thereby helping enhance the lens power of LC lens. In comparison with a pure LC lens, the TiO₂ NP-doped one has approximately 50% lower operation voltage because of the strengthened electric field around the NPs and has roughly 2.8 times faster response time because of the decreased rotational viscosity of the LC mixture and the increased interaction between the LC molecules by the NP dopants. Notably, the doping of rutile TiO₂ NPs improves the operation voltage, tunable focusing capability, and response time of LC lens simultaneously. Meanwhile, this method does not degrade the focusing and lens qualities. The imaging performances of TiO₂ NP-doped LC lens at various voltages are demonstrated practically by tunable focusing on three objectives at different positions. These results introduce NP in the application of LC lenses.