Study on application of UV-processed molecular alignment in liquid crystal devices
Photoalignment technique in liquid crystal devices (LCDs) fabrication processes is classified into a non-contact process which provides an anisotropy in liquid crystal (LC) alignment layer by exposing ultra violet (UV) light. The greatest benefit for using this technique is to avoid electrostati...
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| Format: | Thesis |
| Language: | English |
| Published: |
2011
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| Subjects: | |
| Online Access: | http://eprints.uthm.edu.my/3005/1/24p%20JAIS%20LAIS.pdf |
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| Summary: | Photoalignment technique in liquid crystal devices (LCDs) fabrication
processes is classified into a non-contact process which provides an anisotropy in liquid
crystal (LC) alignment layer by exposing ultra violet (UV) light. The greatest benefit for
using this technique is to avoid electrostatic charges and impurities on the substrate.
Moreover, photoalignment can realize the structures which has the required liquid
crystal director azimuth with the selected area of the cell, thus viewing angle
characteristics can be improved by the pixel dividing. In this study, the photoalignment
technique was applied to the fabrication of a bistable type LCD and polymer-stabilized
blue phase (PSBP) LCD.
Most liquid crystal devices are monostable, which possesses only one possible
state in absence of field. They requires continuous voltage application and frequent
image refreshment, which is the cause of the energy consumption and limits the
multiplexability. In other word, monostable devices have no intrinsic pixel memory and
they need an active matrix or other external storage elements to obtain high
multiplexing levels. Bistable type LCD have two (or more) stable states. Once an image
displayed, the director state in each pixels is memorized for a long time, ranging from
seconds up to years, until when the new image is overwritten. This intrinsic memory
capability is a peculiar advantage of the bistable type LCD, provides a potential to
reduce the power consumption, especially for the specific application which is
unnecessary frequent update. In this study, to fabricate a bistable LCD (BLCD) by using
unpolarized UV light irradiation, single-step laser patterning to photoalignment layer
was proposed. Bistability can be achieved by two equilibrium configurations of LC
director profile which is induced by a periodically patterned alignment layer on a
substrate. The patterns were formed by stripes of alternating random planar and
homeotropic anchoring in the order of 0.5 μm. In this work, two possible configurations
of bistable LCD that can be obtained by combining a micropatterned surface formed
with alternating random-planar- and homeotropic-alignment with planar- or
homeotropic-alignment surfaces were proposed. The alignment properties of the two
proposed BLCD models such as twisted angle, pretilt angle and its microscopic
switching behavior and memory effect were investigated and determined. It was
assumed that the formation of the two bulk orientational states will depend on the
degree of depolarization of the laser light, the stripe periodicity and the effective
anchoring strength of the patterned surface. |
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