In this thesis, various LC/polymer composite films for the application to flexible and transparent displays were reported. LC/polymer composite films such as polymer dispersed LC (PDLC), polymer stabilized LC (PSLC) and phase separated composite films (PSCOF), were primarily used as display devices....
In this thesis, various LC/polymer composite films for the application to flexible and transparent displays were reported. LC/polymer composite films such as polymer dispersed LC (PDLC), polymer stabilized LC (PSLC) and phase separated composite films (PSCOF), were primarily used as display devices. Recently it has been thought that they might be substantive solutions for flexible LCD owing to the good mechanical stability. Mechanical stability, the most critical issue in the flexible LCD, was achieved through the formation of polymer walls in LC layer or the encapsulation of LC materials. For cholesteric LC, the polymer wall formation was effective for achieving good mechanical stability. Polymer walls were clearly formed through the polymerization induced phase separation method (PIPS). With the introduction of the photo-sensitive chiral dopant (PSCD) to the cholesteric LC, the chiral pitch of which was increased by UV irradiation, the selective reflection wavelength of the cholesteric LC cells could be changed by the ultraviolet (UV) irradiation. Using the method, various colors were realized in flexible cholesteric LCD with single LC mixture and layer. The polymer wall formation was introduced to the polarized LC modes such as vertical alignment (VA), twisted nematic (TN), and electrically controlled birefringence (ECB). Polymer walls were formed between the alignment coated substrates, and vertically separate the LC regions. So the LC molecules inside each region were directly contacted with the alignment layer, resulting in the good control of LC alignment. This flexible LCD had good mechanical stability without the deterioration of electro-optical performance. The formation of polymer walls in normally transparent PDLC (NT-PDLC) cell was carried out for LC molecules to directly contact with alignment layer, resulting in good vertical alignment. For the high scattering efficiency, a second UV exposure without the photo-mask was done to form the polymer networks. It was transparent at off state, and switched to opaque state when applying appropriate electric field. This high performance NT-PDLC made by two-step UV exposure would be applicable to the various light shutter devices. Encapsulation of LC materials using emulsion method was developed. For the cholesteric LC mode, a complex coacervation method was introduced to uniformly encapsulate the LCs surrounded by gelatin shells. We attempted to make a soft capsule which had good elasticity and durableness with the addition of surfactant, and then made the coated capsule layer be pressed flat. By controlling of the capsule shape and compactness of LC layer, flexible color cholesteric LCD which had great mechanical stability and bright vivid colors was achieved. For PDLC mode, we tried a modified emulsification method using the membrane filtering technology, where the LC droplet size could be controlled precisely. Using the various LC droplets with different sizes, we could freely design the LC cell configurations with appropriate size distributed single layer and multi layers, which highly influenced the electro-optical properties of PDLC cell. These LC/polymer composite film displays with good mechanical stability and electro-optical performances would be substantive solutions for flexible or/ and transparent displays.
In this thesis, various LC/polymer composite films for the application to flexible and transparent displays were reported. LC/polymer composite films such as polymer dispersed LC (PDLC), polymer stabilized LC (PSLC) and phase separated composite films (PSCOF), were primarily used as display devices. Recently it has been thought that they might be substantive solutions for flexible LCD owing to the good mechanical stability. Mechanical stability, the most critical issue in the flexible LCD, was achieved through the formation of polymer walls in LC layer or the encapsulation of LC materials. For cholesteric LC, the polymer wall formation was effective for achieving good mechanical stability. Polymer walls were clearly formed through the polymerization induced phase separation method (PIPS). With the introduction of the photo-sensitive chiral dopant (PSCD) to the cholesteric LC, the chiral pitch of which was increased by UV irradiation, the selective reflection wavelength of the cholesteric LC cells could be changed by the ultraviolet (UV) irradiation. Using the method, various colors were realized in flexible cholesteric LCD with single LC mixture and layer. The polymer wall formation was introduced to the polarized LC modes such as vertical alignment (VA), twisted nematic (TN), and electrically controlled birefringence (ECB). Polymer walls were formed between the alignment coated substrates, and vertically separate the LC regions. So the LC molecules inside each region were directly contacted with the alignment layer, resulting in the good control of LC alignment. This flexible LCD had good mechanical stability without the deterioration of electro-optical performance. The formation of polymer walls in normally transparent PDLC (NT-PDLC) cell was carried out for LC molecules to directly contact with alignment layer, resulting in good vertical alignment. For the high scattering efficiency, a second UV exposure without the photo-mask was done to form the polymer networks. It was transparent at off state, and switched to opaque state when applying appropriate electric field. This high performance NT-PDLC made by two-step UV exposure would be applicable to the various light shutter devices. Encapsulation of LC materials using emulsion method was developed. For the cholesteric LC mode, a complex coacervation method was introduced to uniformly encapsulate the LCs surrounded by gelatin shells. We attempted to make a soft capsule which had good elasticity and durableness with the addition of surfactant, and then made the coated capsule layer be pressed flat. By controlling of the capsule shape and compactness of LC layer, flexible color cholesteric LCD which had great mechanical stability and bright vivid colors was achieved. For PDLC mode, we tried a modified emulsification method using the membrane filtering technology, where the LC droplet size could be controlled precisely. Using the various LC droplets with different sizes, we could freely design the LC cell configurations with appropriate size distributed single layer and multi layers, which highly influenced the electro-optical properties of PDLC cell. These LC/polymer composite film displays with good mechanical stability and electro-optical performances would be substantive solutions for flexible or/ and transparent displays.
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#Flexible LCD
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