Electro-Optical Properties of In-Plane Switching Vertically Aligned Liquid Crystal Devices with Polymer Networks
Date Issued
2015
Date
2015
Author(s)
Lin, Guan-Jhong
Abstract
Polymer networks are employed in vertically aligned liquid crystal (VA LC) cells to stabilize the LC molecular configuration under the in-plane switching (IPS) electric field driving. Three kinds of polymer morphologies are well developed and anchored on the glass substrate surface. With the planar cross-linking polymer morphology, the transformed electro-optical properties of the cell, composed of positive nematic LC and biphenyl diacrylate monomer, are revealed. As compared to the pure LC cells, this type of LC/polymer cell shows fast switching and gray-level responses at a low driving voltage (≤ 12 V), which is attributed to the increased anchoring effect that effectively governs the LC molecular reorientation. In addition, the alignment transformation and transmittance bounce, resulting from the transient process of LC molecular reorientation, are eliminated when the cell is operated at high voltages. The appropriate display cell considering the driving voltage and response simultaneously is also developed at an optimum mixed concentration of 2 wt.%. Without overdrive, the turn-on response of this cell is comparable to that of the pure cell under overdrive. In order to conserve the power energy and enhance the image performance, a novel and reproducible alignment method for fabricating VA-based LC cells with a multi-pretilt structure is developed. A non-uniform vertical electric field is employed in the optimum IPS-VA LC/polymer cell during the photo-curing process, and two pretilt domains with the functional small pretilt angle (~ 1.6°) in the stabilized IPS-VA LC/polymer cells are achieved. As compared to the pure cell, this proposed cell shows 36%, 64%, and 76% enhancement in the optical-switch, gray-level rise time, and gray-level fall time responses, respectively. This research not only demonstrates a suitable monomer material and its concentration that, applied to IPS-VA LC cells, can benefit the molecular alignment and configuration, but also proposes a new method that effectively reduces the driving voltage and further boosts the device performance.
Subjects
Polymer networks
vertically aligned
in-plane switching
liquid crystal
anchoring
cross-linking
molecular configuration
pretilt angle
response
Type
thesis
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