| 摘要(英) |
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. |
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