| 摘要: | 隨著液晶技術的日趨成熟，液晶元件的研究更是蓬勃發展，而液晶散射光閥便是其中之一。目前最廣受應用的液晶散射光閥為聚合物分散液晶(polymer dispersed liquid crystal, PDLC)，可利用其混合物之單體聚合反應引致液晶與高分子相分離而產生散射，並藉由外加電壓改變此液晶元件的散射態以及穿透態。此外，一般的散射光閥需對元件持續施加電壓方能維持其穿透狀態，在提倡綠色能源的時代持續耗電的元件將陸續被改良，取而代之的便是雙穩態的散射光閥，在利用電壓切換狀態之後，即便關閉其施加電壓亦能維持著穿透狀態，且能利用外加另一電壓而使該穿透態切換回散射態。
本論文使用經濟、環保及其製程簡便的中孔洞氧化矽奈米粒子做為散射體，將其摻入向列型雙頻液晶後，便能得到具有雙穩態效果的液晶散射光閥，另改變外加電場的頻率可使元件在穿透態與散射態之間切換，且電場關閉後仍能維持在穿透態或散射態。本論文將分別討論(1)中孔洞氧化矽奈米球摻雜不同液晶對其穿透率及穩態效應的影響、(2)探討不同配向處理的基板對摻雜中孔洞氧化矽奈米粒子液晶元件的穿透率及穩態效應的影響、(3)中孔洞氧化矽奈米粒子之摻雜濃度對於液晶元件的穿透率及穩態效應影響以及(4)摻雜中孔洞氧化矽奈米粒子對於藍相液晶溫寬的影響。利用中孔洞氧化矽奈米粒子的多孔洞特性能形成液晶分子區塊，使元件內部材料產生折射率不匹配以及不連續進而造成光散射，而中孔洞氧化矽奈米粒子與液晶分子間的作用力會使奈米粒子隨著液晶分子受到電場而轉動。
若中孔洞氧化矽奈米粒子摻雜雙頻液晶，施加低頻交流電能將液晶元件切換至穿透態，而施加高頻交流電則切換至散射態。有關電壓關閉後的穩態效應機制，我們推測是因中孔洞氧化矽奈米粒子周圍液晶分子的分佈，使得中孔洞氧化矽奈米粒子彼此相互排斥而不團聚，此外，排斥力會抵消元件恢復的能量，使液晶元件達到穩態，詳細原理將在本論文後續章節說明。因此，本論所提出之雙穩態電控液晶光閥具有環保與製程簡便等優點，相信未來在生活中的應用具相當之潛力。
;With the continuous growth of liquid crystal (LC) technology, the developments of LC devices have been being paid much attention by scientists. Among them, scattering mode LC light shutter is one of the popular techniques, such as polymer dispersed LCs (PDLCs). One of the scattering mechanisms is based on the formation of LC droplets by means of the polymerization induced phase separation of pre-polymer and LCs. Moreover, the scattering state and transparent state can be switched between each other by applying an external voltage. It should be noted that the continuously applied voltage is required to keep the transparent state. Restated, the transparent state will be switched back to scattering state when the applied voltage is turned off. Regarding the energy saving, the bistable scattering mode LC light shutters are the great candidates to save power, and to replace the devices with the disadvantage of high power consumption. Briefly, the bistable LC devices, which do not require real-time information update and do consume power when the displayed image content needs to be changed. One can apply an external voltage to switch the scattering mode LC light shutter to transparent state, and can also apply another external voltage to switch the transparent LC light shutter back to scattering state.
In this study, mesoporous silica nanoparticles (MSNs)-doped nematic LCs are adopted to demonstrate light scattering. Such an approach provides the advantages of low-cost, environmental protection, and simple fabrication processes. Moreover, the dual frequency LCs doped with MSNs present a bistable scattering mode LC light shutter. It is also demonstrated that the scattering and transparent states can be switched with each other by changing the frequency of the applied voltage. After the applied voltage is turned off, the transmission can be kept stable. The following four topics will be discussed in this thesis, including (1) the effect of various LC materials doped with MSNs onto the transmission and stability performances; (2) the effect of various surface alignment layers onto the scattering mode LC device; (3) the effect of concentration of MSNs onto the scattering mode LC device; and (4) the effect of MSNs onto the existing temperature of blue phase LCs.
Considering the mechanism of light scattering based on MSNs-doped LCs, it can be understood that the doped mesoporous will affect the orientation of LCs so that the LC domains can be generated in the LC cell. Hence, the incident light can be scattered by the LC domains due to the mismatch and the discontinuousness of refractive indices of LC and MSNs. Importantly, we infer that the orientation of the rod-like MSNs will be rotated by the torque produced by the application of external voltage onto the LCs due to the molecular interaction force between the doped MSNs and LCs. To demonstrate the bistable scattering mode LC light shutter, dual-frequency LCs doped with MSNs are employed to obtain the stable scattering and transparent states. Briefly, such a LC device can be switched to transparent (scattering) state by the application of external voltage having relative low (high) frequency since the dual-frequency LCs present positive (negative) dielectric anisotropic LCs with the application of external voltage having relative low (high) frequency. Moreover, we infer that the LCs will distribute around the MSNs so that the MSNs do not be aggregated with each other. Once the orientation of the rod-like MSNs, caused by the LCs, is parallel to the direction of the applied voltage, the stable transparent state can be obtained due to the scales of LCs and MSNs. As the result, the bistable scattering mode LC light shutter reported in this thesis possesses many advantages, such as low power consumption (environmental protection), simply fabrication processes, and so on. We believe that such a bistable LC light shutter has huge potential for application of electronics in the near future. |
