Fast Response and Spontaneous Alignment in Liquid Crystals Doped with 12-Hydroxystearic Acid Gelators

Abstract

The spontaneous vertical alignment of liquid crystals (LCs) in gelator (12-hydroxystearic acid)-doped LC cells was studied. Gelator-induced alignment can be used in both positive and negative LC cells. The electro-optical characteristics of the gelator-doped negative LC cell were similar to those of an LC cell that contained a vertically aligned (VA) host. The rise time of the gelator-doped LC cell was two orders of magnitude shorter than that of the VA host LC cell. The experimental results indicate that the gelator-induced vertical alignment of LC molecules occurred not only on the surface of the indium tin oxide (ITO) but also on the homogeneous alignment layer. Various LC alignments (planar, hybrid, multistable hybrid, and vertical alignments) were achieved by modulating the doped gelator concentrations. The multistable characteristic of LCs doped with the gelator is also presented. The alignment by doping with a gelator reduces the manufacturing costs and provides a means of fabricating fast-responding, flexible LC displays using a low-temperature process.

Keywords: alignment; fast reponse; gelator; liquid crystal; multistable property.

Figure 1

Chemical structure of 12-hydroxystearic acid (12-HSA).

Figure 2

Polarized optical microscopy (POM) images of (a) pure liquid crystals (LC) HFW59200-200; (b) 0.1 wt %-12-HSA-doped HFW59200-200; (c) pure LC E7; and (d) 0.1 wt %-12-HSA-doped E7 cells, obtained between crossed polarizers.

Figure 3

POM images of (a,b,e,f) 0.1 wt %-gelator-doped negative dielectric LC LCT-06441 and (c,d,g,h) VA host LC cells; (a–d) and (e–h) are images of samples without and with rubbing, respectively.

Figure 4

Electro-optical curves of 0.1 wt %-gelator-doped negative LC LCT-06441 (red squares) and VA host LC (blue diamonds) cells.

Figure 5

Transmission of 0.1 wt %-gelator-doped LCT-06441 and VA host LC cells positioned between two polarizers, with the analyzer axis rotated relative to the polarizer axis. Angular dependence of the transmission under applied voltages of (a) V = 0 V and (b) V = 10 V.

Figure 6

Optical transmittance of 0.1 wt %-gelator-doped LCT-06441 and VA host LC cells under a step-voltage driving scheme with a step maintenance time of 3 ms.

Figure 7

(a) Electro-optical curves; (b) phases; and (c) POM images of positive LCs (HFW59200-200) doped with various gelator concentrations.

Figure 8

Schematics of LC orientations after doping with the gelator. (a) Planar, (b) hybrid, (c) multistable hybrid, (d) vertical orientations.

Figure 9

Multistable T–V curves of HFW59200-200 cells doped with various gelator concentrations. The transmittance was measured without an applied voltage.