彎曲型氫鍵液晶及其奈米複合材料之超分子作用力研究

Abstract

彎曲型液晶是不具旋光中心結構卻具有光學活性及自發極化能力的液晶材料，本研究著重於氫鍵超分子引入至彎曲型液晶結構時，所產生的液晶性質與光電性質的影響。分子設計上分為：含氫鍵之彎曲型液晶超分子與分歧的矽氧基團的影響、氫鍵之彎曲型液晶超分子與奈米金粒子所形成奈米複合材之影響、含醯胺之棒狀及彎曲型液晶混掺效應討論，總共分為三個章節在本文中討論。 由研究結論得知，一個具有氫鍵及分歧矽氧的基團之彎曲型液晶，存在一系列的具雙傾斜性質及高規則層列結構，我們首先由及時施加電廠及廣角X光的觀測方式，在降溫過程中，觀查出leaning angle由60縮小至50°，並藉著紅外線及拉曼光譜儀，在不同溫度中偵測出氫鍵及分歧矽氧的基團之作用力，除此之外， 不同的鐵電性質(鐵電-反鐵電-鐵電)，也可以在具雙傾斜性質的液晶分子量測得知。 以氫鍵之彎曲型液晶為主，可藉由混摻不同濃度的金奈米粒子(客)的奈米複合材料，可改變不同的液晶特性，隨著增加的金奈米粒子的添加，其鐵電特性可由反鐵電、鐵電改變至無任何電性，並由及時施加電廠及廣角X光的觀測方式， 使奈米複合材中的氫鍵之彎曲型液晶及金奈米粒子，有著規則的層狀排列，為了保持液晶在電廠下的規則排列，利用液態氮固化樣品，最後利用穿透式電子顯微鏡觀測出金奈米子規則排列的行為。 合成出具有醯胺之棒狀、彎曲型液晶分子及以脂基為連結基的彎曲型液晶分子，為了比較不同強度的氫鍵側向作用力，混掺不同比例之棒狀及彎曲型液晶在醯胺彎曲型液晶與之棒狀分子為3:7時，反鐵電層列C相可以被觀察出，所以就混摻系統而言，在特定比例下，棒狀分子可以誘導出具鐵電特性的液晶。

Bent-core liquid crystals are achiral structures with spontaneous polarization and chirality properties. In this thesis, the identifications and classifications of banana-phase types, electro-optical properties, and bent-core structural configurations were introduced. Meanwhile, the influences of H-bonded interaction and in bent-core supramolecular materials and its nanocomposites on the mesomorphic and electro-electric properties were investigated in this doctoral thesis as well. In chapter 2, a hydrogen-bonded complex with a branched siloxane units exhibited a series of general tilt smectic (SmCG) phases with highly ordered layer structures. As the SmCG domains were aligned under dc electric fields, a gradual decrease in the leaning angle from ca. 60 to 50° could be determined by in-situ wide-angle X-ray scattering (WAXS). Combined with Fourier transform infrared and Raman spectroscopic data, our results suggest that the change in the leaning angle was governed by the competition of the hydrogen bonds and microsegregation of siloxane units within the bilayer structure of the hydrogen-bonded complex with a branched siloxane units. In addition, the ferroelectric–(anti-ferroelectric)–ferroelectric transitions proven by the switching current responses in the SmCG-type phases. In chapter 3, in this study we prepared novel nanocomposites from the hydrogen-bonded bent-core liquid crystal (LC) host and different weight ratios (0–20 wt%) of the surface-modified gold nanoparticles. The mesomorphic properties of the nanocomposites, including their mesophasic types and ranges, values of Ps, and dielectric constants, were adjustable by varying the doping concentrations of gold nanoparticles. By increasing the concentration of gold nanoparticles , the polarity of the SmCP phase in the nanocomposite varied sequentially from anti-ferroelectricity sequentially to ferroelectricity and to nonpolarity. Furthermore, the molecular stackings and layer arrangements of the LC molecules were aligned parallel and perpendicular to the electric fields, respectively, as confirmed from the associated X-ray diffraction patterns. Direct evidence from transmission electron micrographs revealed that the well-organized layer packings of the surface-modified gold nanoparticles in the nanocomposites could be induced under electric fields. In chapter 4, novel liquid crystalline materials with rod-like molecules bearing amide group, bent-core molecules containing all ester groups and amide groups have been synthesized. The influence of blending system for binary systems was studied by lateral H-bonded interactions. An antiferroelectric switching smetic C phase was found for the complex rod-like molecules / bent-core molecules with amide groups = 3/7. Therefore, rod-like liquid crystal bearing an amide linkage induced the polar switching behaviors of bent-core liquid crystalline with amide groups.