High-Density Poly(methyl methacrylate) Brushes as Anchoring Surfaces of Nematic Liquid Crystals

Abstract

The orientation of a nematic liquid crystal (LC) on high-density poly(methyl methacrylate) (PMMA) brushes was examined. The nematic LC was injected into the cell consisting of two substrates on which PMMA chains were grafted with a density of 0.299 chains nm-2. It showed degenerate planar orientation, which became uniform on cooling from 120 °C at a magnetic field of 1 T. At ambient temperature, the aligned LC cell showed typical electro-optical properties when driven in the in-plane switching (IPS) mode, indicating that the LC molecules anchored to the brushes with the director parallel to the magnetic field direction. In contrast, at temperatures higher than 65 °C, the transmittance of the cell was time-dependent when driven over a prolonged period, suggesting that the anchoring direction rotated toward the electric field direction. Such temperature-dependent anchoring of the LC can be associated with the viscoelasticity of the PMMA brushes.

Effect of dye structure on orientational behavior and transition dipole moments in coatable guest–host polarizers

“…The alignment layer was prepared by coating AL16301 (JSR Co.) on glass. AL16301 is suitable for achieving a parallel homogeneous alignment [17][18]. The spin-coating was performed at 700 rpm or 1100 rpm for 10 s. The spin-coated samples were stabilized by curing at 100 o C for 3 min.…”

Optimized molecular structures of guest–host system for highly efficient coatable polarizer

“…The alignment layers were prepared by coating AL16301(JSR Co.) on glass. AL16301 is suitable for achieving a parallel homogeneous alignment [20][21]. The spin-coating was performed at 1100 rpm for 10 sec.…”

Viscoelastic PS brush surface offering strong anchoring at low temperature and near-zero anchoring at high temperature for LC molecules

“…The uniform orientation of the molecules in the PS-B cell was accomplished by the same technique as used for the PMMA-B cell [9]. The nematic LC injected into the PS-B cell exhibited schlieren texture under POM (Figure 2(a)), indicating the notable trend that the nematic LC on the PS brushes had a planar orientation similar to that observed on the PMMA brushes.…”

“…The nematic LC injected into the PS-B cell exhibited schlieren texture under POM (Figure 2(a)), indicating the notable trend that the nematic LC on the PS brushes had a planar orientation similar to that observed on the PMMA brushes. Although the reason for this preferred planar orientation is still unknown, it is speculated that the segments of the brushes away from the base are parallel to the substrate causing the LC molecules to primarily interface with the side of the brushes, thereby orienting themselves parallel to the surface [9]. The homogeneous LC alignment in the cell presented in Figure 2(b) was achieved by heating the cell to the isotropic melt temperature of 120 • C and then cooling it to ambient temperature at the rate of 3 • C min −1 under a magnetic field of 1 T. Figure 3(a) shows the voltage-light transmittance curves of the PS-B and RPI cells driven in the IPS mode at 25 • C. Here the cell was set originally such that the nematic LC director coincided with the polariser direction leading to complete darkness, and the transmittance is represented as the relative values taking the transmittance value in the electric field-off state and at maximum field strength as 0 and 100%, respectively.…”

“…On increasing the temperature, however, the transmittance became time dependent, suggesting that the LC molecules anchored to the brushes rotated towards the direction of the electric field. At high temperatures, the brushes were thus considered to function as 'soft' anchoring surfaces for the nematic LC [9].…”