| 摘要: | 在液晶顯示器及液晶元件的應用中，控制液晶分子排列的方式在學術研究上以電控、光控及熱控為主，而藉由表面聲波改變液晶排列的研究則相對稀少許多，因此本論文的研究將嘗試藉由表面聲波改變液晶分子的排列方式，研究主題主要研究膽固醇液晶分子排列受表面聲波影響產生的改變，第一部分藉由表面聲波致膽固醇液晶分子排列自焦錐態(Focal conic textures)切換至平面態(Planar textures)，實驗中以向列型液晶(E7)及手性分子(CB15)混和為膽固醇液晶，當使用壓電材料搭配叉指電極(Interdigital transducers, IDTs)產生表面聲波輸入至液晶盒時會同時產生熱能，此時膽固醇液晶分子同時受到表面聲波及熱的影響而出現排列擾動的現象。表面聲波進入液晶盒會形成聲流場，實驗結果證明若聲流場在液晶盒中持續影響一段時間後關閉表面聲波，液晶分子會自起始的焦錐態切換為平面態結構，如將持續時間拉長且在表面聲波強度足夠下，液晶分子會因溫度上升而相變至澄清態，實驗中在未控溫下藉由叉指電極輸出不同強度的表面聲波並維持不同的持續時間，將顯微鏡下觀測圖及其頻譜圖記錄下來並做討論，表面聲波的強度與液晶重新排列的速率呈現正相關。第二部分的研究使用與第一部分相同的膽固醇液晶注入上下基板皆為玻璃基板的液晶盒，將其置於控溫器中觀察並記錄溫度的變化對膽固醇液晶分子排列的影響，並將第二部分和第一部分的實驗做比較，由實驗結果可證實溫度並非造成焦錐態切換成平面態的主要原因。第三部分的研究使用與第一部份實驗相同的液晶盒，利用溫控器控制液晶盒溫度以降低生成表面聲波時產生的熱效應，探討表面聲波對膽固醇液晶排列結構的影響，在控溫下液晶仍可透過表面聲波自焦錐態切換為平面態。;Due to the unique optical properties, liquid crystals (LCs) have been widely used in various optical fields and electronics. There are lots of considerable studies of the changes of LC arrangements through optical, electrical, and thermal manners. However, the researches in changing LC arrangements by surface acoustic waves (SAWs) are relatively rare. Therefore, the changes of LC arrangement by feeding SAWs into LCs will be studied experimentally in this thesis. The thesis concentrates on the changes of cholesteric LCs (CLCs) arrangement by the applications of SAWs. The CLCs used herein are composed of nematic LC (E7) and chiral dopant (CB15). The experiments are divided into three parts. In the first part, the changes of CLCs textures from focal conic textures to planar ones by feeding SAWs through substrates made by LiNbO_3 at room temperature without temperature control are studied. However, heat is generating when the substrates is generating SAWs by the applications of electric field onto the IDTs. CLC arrangements are affected by the generated heat and SAWs. Supposing CLCs are initially in focal conic textures, the experimental results show that the acoustic streaming generated by SAWs makes the CLCs form a CLC flow. With the application of SAWs onto CLCs for a suitable duration, the CLCs can be transformed from focal conic to planar textures. To keep the obtained planar textures, the electric filed applied onto the IDTs should be switched off. However, the CLCs will become isotropic state due to thermal effect if the duration of the application of SAWs is long enough. In the experiments, SAWs, generated by the application of electric filed, including 15.3, 23.8, and 38 Vpp@20 MHz, onto IDTs for different durations at room temperature without temperature control are used. The observations under a microscopy and the transmission spectra are recorded for discussion. Experimentally, the strength of SAWs is positivity correlated with the rate of LCs rearrangement. In the second part, the CLCs consistent with that used in the first part are injected into a LC cell whose substrates are assembled by two glass substrates, and then, the effects of thermal onto the arrangement of CLC molecules are examined with temperature control by a hot stage. Refer to the experimental results, we confirm that the switch of CLC textures from focal conic textures to the planar ones is about independent of temperature. In the finally part, the same CLCs are injected into a LC cell, consistent with that adopted in the first part. The effect of SAWs onto the CLC arrangement is discussed. A temperature controller is adopted to minimize the influence of SAWs-induced heat onto CLC arrangement. According to the experimental results, the CLCs with temperature control can still be switched from focal conic textures to planar ones through the applications of SAWs. |
