Poly Vinyl Cinnamate Films Research Articles

Anisotropic Shear Viscosity of Photoaligned Liquid Crystal Confined in Submicrometer-to-Nanometer-Scale Gap Widths Revealed with Simultaneously Measured Molecular Orientation.

In the context of the use of liquid crystals (LCs) as lubricants and lubricant additives, this study investigates the anisotropic shear viscosity of LCs confined in nanometer-sized gap widths subject to both shearing and photoalignment. The photoalignment is achieved using anisotropically dimerized polyvinyl cinnamate (PVCi) films coated on substrates. We simultaneously measure the viscosity and order parameter of a liquid crystal (4-cyano-4'-pentylbiphenyl) confined and sheared in the gap range of 500 nm down to a few nm. We achieve this simultaneous measurement using an original method that combines a highly sensitive viscosity measurement and a sensitive birefringence measurement. When the LC is sheared in the same direction as the photoalignment (parallel shearing), the order parameter, which is around 0.3 in the bulk state, increases up to around 0.4 at a gap width of less than 50 nm and the viscosity is smaller than half the bulk viscosity. We consider that this increase in the order parameter is due to the highly ordered photoaligned LC layer near the PVCi film, and the viscosity decrease is due to shear thinning of this layer enhanced by both confinement and molecular ordering. In addition, we observe a gradual decrease in viscosity starting at a gap of less than around 300 nm in the parallel shearing. Based on the apparent slip model, we show that the LC layer near the PVCi film can also cause this gradual viscosity decrease. In contrast, when the LC is sheared in the direction perpendicular to the photoalignment direction (perpendicular shearing), the viscosity increases as the gap decreases. We speculate that this is due to the rotational motion of the LC molecules caused by the competing effect of shear alignment and photoalignment. We believe our findings can significantly contribute to a better understanding of the confined LCs utilized for lubrication.

Electrically Aligned Photo-Polymer Films for Liquid Crystal Alignment

The photo and electric field alignment of thin film of polyvinylcinnamate (PVCN) is shown to be considerably enhanced by using a combination of both methods. ITO-coated glass substrates were covered with a PVCN film using spin or dip coating and then heated above the glass transition temperature of PVCN. The alignment was induced by applying an electric field and stabilized by [2+2] cycloaddition of the polymer using a linearly polarized UV light. The anisotropy of the aligned polymer films was checked by measuring linear birefringence. Without crosslinking, the anisotropy of the electrically aligned films is very weak. Crosslinked PVCN films using polarized UV light in the absence of any external fields lead to a better anisotropy than the aligned film by an electric field. The anisotropy is however increased substantially when the aligned PVCN films were crosslinked in the presence of a field.

Liquid crystal alignment on photopolymer surfaces exposed by linearly polarized uv light.

A photo-alignment of nematic liquid crystals (NLC) on a photopolymer film of polyvinyl cinnamate (PVCi) has been achieved by using linearly-polarized UV light. The mechanism of the LC alignment is clarified and good unidirectional LC alignment with pretilt angle is obtained by appropriate combination of normal and oblique exposure of linearly-polarized UV light to the PVCi films. This photo-alignment method is applied to fabricate super-multidomain (SMD) TN-LCDs making a feature of quartered pixels, and we demonstrate that reverse tilt disclination (RTD)-free SMD TN-LCDs is successfully fabricated by using the photo-alignment method.