共價鍵結構混摻香蕉型氫鍵液晶分子之效應

Abstract

本實驗取了五環的香蕉型共價鍵液晶分子分別與五環的香蕉 型雙氫鍵及單氫鍵液晶分子混摻，並做偏光顯微鏡(POM)，示差掃描 熱量計(DSC)，X-ray 粉末射線繞射儀 (Powder-XRD)，介電分析，以 及三角波法做光電量測並探討其性質。比較之下共價鍵液晶混入單氫 鍵液晶效果較佳，所有的混合物都具有SmCP phase，而混入雙氫鍵 液晶需要超過50 wt%共價鍵液晶才有。 另外，混入液晶相較廣之共價鍵分子可以大幅增廣該系列混摻物 之液晶相範圍，且碳鏈較長的共價鍵分子比碳鏈較短的共價鍵液晶的 分子對混摻物的影響較大，即在較少共價鍵比例下有該系列最廣的液 晶相，而且較少的共價鍵則可降低Ps 值的飽和電壓。 再者，混摻物d-spacing，domain 大小，Ps 值都與混摻比例有關， 尤其是Ps 值在單氫鍵與共價鍵混摻系列上幾乎呈線性關係，故可以 經由調整混摻比例達到所希望的Ps 值。

In order to improve the properties of H-bonded bent core mesogens, mixtures of single/double hydrogen bonded banana-shaped compound doped with covalent bonded banana-shaped liquid crystals were studied. The phases were demonstrated by polarized light optical microscopy (POM), differential scanning calorimetry (DSC), powder X-ray diffraction (XRD), and electro-optical properties based on dielectric responses as well as measurements of polarization reversal currents. The temperature ranges of the B2 phase of mixtures were extended from a few degrees to forty degrees due to the contribution of covalent-bonded LCs. Moreover, the spontaneous polarization (Ps) values of single H-bonded LCs were increased by increasing the percentages of the covalent-bonded mesogens linearly. The relationship between Ps values and applied voltages were also studied. Compared with covalent-bonded LCs, saturated applied voltages can be reduced by blending H-bonded mesogens with covalent-bonded LCs. On the other hand, the antiferroelectric properties of H-bonded LCs were improved and stabilized by doping with covalent-bonded LCs.