23.4: Electro‐Optic Properties of Ferroelectric Nanoparticle / Liquid Crystal Dispersions

Abstract

We enhance the electro-optic performance of liquid crystals by dispersing ferroelectric nanoparticles. Devices using these dispersions have lower driving voltages, faster switching speeds and higher contrast ratios. These changes are caused by increases in the dielectric anisotropy, birefringence and elastic constants and can be used to produce improved displays.

Characterization of BaTiO3 Nanoparticles Suspension in Liquid Crystal

“…However, none of the BT-NP/LC suspensions showed a significant change from their original characteristics. The difference between our experiment and the previous ones [11][12][13] is the fabrication process of the BT-NP/LC suspension. We used originally nanosize particles, and did not use any solvent or surfactant.…”

“…Therefore, we did not require an evaporation process to remove the solvent. In contrast, in a previous work, in which a large change in T NI was observed, heptane and oleic acid were used as a solvent and surfactant, respectively, and an evaporation process was necessary to remove heptane after mixing the LC with the suspension of BT-NPs in heptane [11][12][13]. Commercially available LCs are mixtures of several kinds of single-component LCs to control their properties.…”

“…In previous works [11][12][13] a solvent and surfactant were used to prepare stable BT-NP suspensions in the LC; however, it was difficult to completely remove them from the suspensions. To prevent side effects due to their presence, we prepared BT-NP suspensions without using any solvent or surfactant.…”

“…Before dispersing BT-NP in the LC, they were dried in a vacuum oven at 100 °C for 2 h. After drying, they were mixed with the LC and sonicated by a tip sonicator (Branson, Sonifier 250) while being heated to the isotropic phase. The LC used for this experiment was the negative-Δε epsilon$ LC used in previous reports [11][12][13] with T NI = 91.5 °C and Δε= -3.7 at 20 °C.…”

“…However, the current trend of exhibiting three-dimensional images requires a higher frame rate and a higher speed response to liquid crystals (LCs). To meet these requirements, improvement of the characteristics of LCs by doping a low concentration of nanoparticles, such as carbon nanotubes (CNTs) [1,2], metals [3][4][5][6][7], metal oxides [7][8][9][10], and ferroelectric materials [11][12][13][14][15] has been reported. Among these nanoparticles, ferroelectric nanoparticles consisting of barium titanate (BaTiO 3 ) induce significant changes in the phase change temperature (T NI ) of LCs and their threshold voltage (V th ) upon doping them into LCs [11].…”