Homeotropic Polyimide Surface Research Articles

Correlations Between the Surface Energy and the Tilt Angle on the Homeotropic Polyimide Surface

We investigated the correlations between the surface energy and the tilt angle on homeotropic polyimide (PI) surfaces subjected to rubbing using ion beam (IB) irradiation. The tilt angle of nematic liquid crystal (NLC) decreased with increased rubbing times. Also, the tilt angle of NLC was measured to be homeotropically aligned and then rapidly changed to homogeneous alignment with increasing IB irradiation time. We assumed that the LC alignment depends strongly on the C–O bonds created from bonds on the PI surface broken with IB irradiation, which was confirmed through X-ray photoelectron spectroscopy measurements. In addition, the contact angle on the PI surface decreased with increasing IB irradiation time. Therefore, we conclude that the IB irradiation is attributed to the high surface energy and the compositional variation of the homeotropic PI, resulting in a transition of NLC orientation.

Tilt Angle Generation in NLC on Homeotropic Polymer Surface with Ion Beam Irradiation as a Function of Incident Angle

We have studied the tilt angle generation on the homeotropic polyimide (PI) surface using a low intensity ion beam source as a function of incident angle. An excellent LC alignment of nematic liquid crystal (NLC) on the PI surface with ion beam exposure for all incident angles was observed. The tilt angle of NLC on the homeotropic PI surface for all incident angles was from 90 to 88 degree was observed. Also the tilt angle of NLC on the homeotropic PI surface with ion beam exposure of 400 eV had a tendency to increase as ion beam energy incident angle become more instance from 45 degree. Finally, a good LC alignment thermal stability on the homeotropic PI surface with ion beam exposure can be achieved.

LC Aligning Capabilities of a Nematic Liquid Crystal on Homeotropic Polyimide Surface by New Ion-beam Irradiation

The liquid crystal(LC) aligning capabilities of a nematic liquid crystal(NLC) on a homeotropic polyimide(PI) surface using a new ion-beam method were studied. Exposure ion-beam of <TEX>$45^{\circ}$</TEX> incidence angle shows a good LC alignment of the NLC on the homeotropic PI surface. Also, on the homeotropic PI surface, the tilt angle of the NLC by exposure ion-beam of <TEX>$45^{\circ}$</TEX> incidence angle had a tendency to decrease as increased ion-beam energy density. And, on the homeotropic PI surface, the alignment character of the NLC with respect to ion-beam energy was good at 1500 eV. And we achieved satisfactory result for EO character.

Liquid Crystal Alignment Effects for Nematic Liquid Crystal on Homeotropic Polyimide Surface Using New Ion-Beam Source

We have studied the liquid crystal (LC) alignment and tilt angle generation of a nematic liquid crystal (NLC) on a homeotropic polyimide (PI) surface using a new ion beam source. The tilt angle of the NLC on the homeotropic PI surface for all incident angles is about 38° and this angle has a stabilization trend. A good LC alignment of the NLC on the homeotropic PI surface by to exposure ion beam of 45° incidence angle was observed. Also, the tilt angle of the NLC on the homeotropic PI surface by to exposure ion beam of 45° incidence angle had a tendency to decrease as ion beam energy density increased. Thus, we demonstrated that the tilt angle could be controlled from vertical to horizontal directions. Also, the alignment character of the NLC on the homeotropic PI surface with respect to ion beam energy was good at more than 1500 eV. Finally, a superior LC alignment thermal stability on the homeotropic PI surface subject to ion beam exposure was achieved.

Four-domain twisted vertically aligned liquid crystal pixels using microrubbing

Microrubbing (μ-rubbing) technique is used to create four-domain twisted vertically aligned liquid crystal pixels for wide viewing angle displays. A metallic sphere of 1 mm diameter is used to locally rub a homeotropic polyimide surface to create a four-domain pixel. We use μ-rubbing to accurately control the surface pretilt angle of the liquid crystal from the normal, which directs the liquid crystal molecules to respective direction on applying a voltage. We report on twisted vertically aligned configurations with symmetric isointensity curves, high contrast, and attractive electro-optic performance. The optical simulations of the liquid crystal director orientation, viewing angle characteristics and switching behavior of the four-domain are also presented.

High pretilt four-domain twisted nematic liquid crystal display by microrubbing: Process, characterization, and optical simulation

A microrubbing (μ-rubbing) technique was utilized to create four-domain alignment in a liquid crystal display sample. A small metallic sphere under sufficient load was used to directly rub a homeotropic polyimide alignment layer to create a large surface pretilt angle. We demonstrate a 47-μm linewidth and a variable pretilt angle with respect to the substrate plane for different loads. The homeotropic polyimide surface was μ rubbed in such a way that neighboring alignment regions are rubbed in opposite directions. liquid crystal cells were constructed with two μ-rubbed substrates where the rubbing directions are orthogonal to each other. With this cell configuration we obtained four domains consisting of two left-handed and two right-handed twisted nematic subpixels. We report on the electro-optic performance properties, viewing angle characteristics, the relationship between pretilt angle versus load, and thermal aging study of the four-domain liquid crystal cell. The optical simulations of the liquid crystal director orientation, viewing angle characteristics, and the contrast ratio of the four domains are also presented. The experimental results are in agreement with the simulation results.

P-127: Multidomain Twisted Vertically Aligned Display by Microrubbing and its Simulations

A microrubbing (μ-rubbing) technique is used to create multidomain vertically aligned liquid crystal pixels for wide viewing angle liquid crystal display (LCD) applications. A metallic sphere of 1 mm diameter is used to rub a homeotropic polyimide surface to manipulate the local pretilt angle to create a four-domain pixel configuration. We use μ-rubbing to accurately control the surface pretilt angle of the liquid crystal from the normal, which directs the liquid crystal molecules to respective direction on applying a voltage. We report on the twisted vertically aligned (TVA) configurations showing symmetric isointensity curves, high contrast and attractive electro-optic performance parameters. The viewing angle and electro-optical characteristics are simulated and compared with the experimental results.

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The control of tilt angle for nematic liquid crystal (NLC) with negative and positive dielectric anisotropy on the rubbed homeotropic polyimide (PI) using baking method by hot plate equipment was investigated. LC tilt angle decreased with increasing baking temperature and time. Especially, the low LC tilt angle of positive type NLC (Δ<TEX>$\varepsilon$</TEX>＞0) on the rubbed homeotropic PI surface by increasing temperature and time was measured. The tilt angle of positive type NLC(Δ<TEX>$\varepsilon$</TEX>＞0) is smaller than that of the negative type (Δ<TEX>$\varepsilon$</TEX>＞0) on rubbed PI with increasing baking temperature and time. We consider that the tilt angle of NLC is decreased due to increasing the steric interaction between horizon component of permittivity <TEX>$\varepsilon$</TEX> = of NLC and the stress of polymer side chain by high temperature. As the increase of baking temperature, we obtain that AFM (atomic force microscope) image of rubbed PI surface using Hot-plate method has formed better solid micro-groove structure than oven method.

Tilt Angle Generation for Nematic Liquid Crystal on Blended Homeotropic Polyimide Layer Containing Trifluoromethyl Moieties

A decrease in tilt angle generation for a nematic liquid crystal (NLC) with negative dielectric anisotropy on a blended homeotropic polyimide (PI) surface containing trifluoromethyl moieties was investigated. The decrease in tilt angle (below 90°) of NLC on the blended PI surface containing a homogeneous PI structure having a high tilt angle was measured, and the tilt angle of the polymer was found to decrease as the rubbing strength increased. However, the decreases in tilt angle (about 90°) of NLC on the blended PI homeotropic surface containing two kinds of homogeneous PI structure having a low tilt angle were not observed. The tilt angle of NLC generated was about 73° and the drop of tilt angle is attributable to the trifluoromethyl moiety attached to the lateral benzene ring in the backbone structure on the blended homeotropic PI surface. Therefore, the drop of the tilt angle of NLC to below 90° of NLC can be achieved using the blended homeotropic PI surface.

Response time mechanism for a photo-aligned vertical-alignment liquid crystal display on a homeotropic alignment layer

The electro-optical characteristics of the photo-aligned vertical-alignment liquid crystal display (VA-LCD) with a non-polarized UV exposure of 45° on homeotropic polyimide (PI) surface was investigated. The domain size of the photo-aligned VA-LCD increases proportionately with the UV exposure time. The LC alignment of the photo-aligned VA-LCD is attributed to photo-dissociation of the polymer by UV exposure on the homeotropic PI surface. Good voltage-transmittance characteristics of the photo-aligned VA-LCD without negative compensation film was measured. The response time of the photo-aligned VA-LCD was slow compared with a rubbing-aligned VA-LCD; this is considered to be due to the alignment of LC molecules.