Application of TiO2 nanoparticle and polyimide blend alignment layer in liquid crystal lens

Abstract

Suspension of colloidal nanoparticles (NPs) in liquid crystals (LCs) is a common technology to modify the electro-optical characteristics of a LC device. Unfortunately, NP aggregation spontaneously proceeds over time through the dipolar attractive interaction between NPs and results in the light scattering and distortion of the nematic order, which degrades the performance of the LC device. Here, rutile titanium dioxide (TiO2) NPs were suspended in the alignment layer rather than LCs to prevent the proceeding NP aggregation. During the deposition of the alignment layer, the NPs were hardened in the alignment layer with a hard bake process. The blend alignment layer was utilized to develop a hole-patterned liquid crystal (HLC) lens. This layer enhances the polar anchoring of LCs because of the intermolecular interaction between NP and LC and reduces the ion density and rotational viscosity of the LC mixture through harvested effect of free-ions. It also assists in spreading the fringing electric field toward lens center by TiO2 NP contribution. These results speed up the dynamic response of the HLC lens. The introduction of blend alignment layer decreases the focus and defocus times of the HLC lens by 15% and 34%, respectively. Moreover, the operation voltage of the HLC lens for achieving the shortest focal length is reduced by ∼40%. The decreased switching time is verified by calculating the transient phase conversions of HLC lenses with various viscosities. The calculated results correspond to the experimental results. The blend alignment layer did not degrade the lens and focusing qualities of the HLC lens. Long-term observation revealed that the NP aggregation state remained similar for the LC sample with NPs suspended in the alignment layer. By contrast, NP aggregation spontaneously proceeded and connected networks appeared with time for the LC sample with NPs suspended in LCs. The blend alignment layer can improve the operation voltage and dynamic response of a LC device and prevent device deterioration over time.