The electro-optical performance of nematic liquid crystals (NLCs) dispersed with gold nanoparticles (GNPs) was investigated in this study. The addition of a small amount of GNP dopant decreased the threshold voltage for LC reorientation due to the decreased elastic constant and increased dielectric anisotropy of the LC mixture. The response time of the LC cell was decreased with the addition of tiny amounts of GNPs because of decrease in rotational viscosity of LCs. The doped GNPs also shorten LC reorientation angle during voltage switching, further decreasing the response time of the LC cell. The addition of high amounts of GNPs slowed down the response time of the LC cell, because excess GNPs aggregated and formed networks in the cell, thus disturbing LC alignment and hindering LC reorientation. The measured dielectric spectra of the GNP-LC mixture revealed that the addition of GNPs decreased the relaxation time constant of the LCs. This result confirmed that the GNP dopant decreased the rotational viscosity and elastic constant of the LCs.

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.

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.

A novel, to the best of our knowledge, tunable multifocal liquid crystal microlens array (TMLCMA) was fabricated with a triple-electrode structure consisting of a large-hole, a small-hole array, and planar electrodes. The electro-optical performances of the TMLCMA are characterized, demonstrating the monofocal convex, multifocal convex, and multifocal concave functions when the TMLCMA is manipulated with various driving schemes. Furthermore, the homogenization of a laser beam is realized using the fabricated TMLCMA. The multifocal convex and multifocal concave functions of the TMLCMA successfully suppress the lattice phenomenon caused by the monofocal microlens array, homogenize the Gaussian beam to a flattop intensity distribution, and broaden the beam size.