近年來，液晶材料在顯示科技領域中已被廣泛的應用，幾近取代傳統映像管顯示器所佔有的商業地位，但這些應用與研究仍然屬於針對液晶材料的電性分析，或是利用改質方式來提升其電特性。本研究目的在於利用介電頻譜的量測工具，根據C. W. Oseen、H. Zocher和C. F. Frank等人所提出的液晶連續彈性體理論，針對樣品幾何參數的改變，分析向列型液晶E7在外加磁場下其分子的動力行為，再利用液晶分子的光學折射率異向性，來驗證頻譜分析得到的結果。
在介電頻譜的量測實驗中，所使用的儀器為 Agilent E4980A LCRMeter，量測的頻率範圍在20~2M Hz之間。實驗的過程中，本研究利用實驗室自製的電磁鐵對液晶樣品施加一垂直液晶樣品面的常磁場，並透過LabView程式來自動化操控實驗儀器進而量測實驗數據。而光學量測的部分，則是利用波長為632.8 nm的He-Ne Laser，藉由起偏器產生線偏振光後，利用光檢測器來量測外加場前後，穿過樣品的雷射光偏振變化。
根據量測98 μm和9 μm兩種厚度樣品在外加偏壓與外加磁場下各別的介電頻譜，本研究討論介電頻譜對液晶樣品的物理意義，並分析介電頻譜隨不同的外加場變化以及不同的樣品厚度下，樣品中液晶分子的動力行為機制，且估計出98 μm樣品與9 μm樣品對磁場變化的臨界場大小分別約為500 Oe和3000 Oe。本研究針對98 μm樣品探討不同頻率下，隨外加磁場變化的介電實部，根據Freedericks的理論計算以及向列型液晶E7分子的磁化率異向性，來分析樣品內部液晶分子的動力行為。在介電實部隨磁場變化量測的過程中所觀察到液晶分子隨磁場的弛豫現象，本研究藉著量測開啟或關閉外加磁場後，98 μm樣品介電實部隨時間的變化，得知液晶分子隨磁場反應有類似指數型遞增或衰減的趨勢，因此利用指數增加與遞減函數對量測得到的數據進行適配，進而計算出液晶分子在不同外加磁場強度下的弛豫時間。最後利用光學量測的方式，搭配液晶本身光學折射率異向性的分析，來驗證頻譜量測結果的液晶分子動力行為，並由改變不同量測點間隔時間的實驗結果，印證本研究在介電頻譜分析所觀察到液晶隨外加磁場弛豫現象的結果。

Liquid crystal has been well known as an electro-optical material because of its favorable properties. Most of the studies focused on improving its electro-optical properties, such as response time, driving voltage, etc. The magneto-dielectric relaxation behaviors have not yet been well clarified. Therefore, in this thesis, we study these interesting properties of E7 liquid crystal using dielectric spectroscopy method.
The dielectric spectra are measured by an LCR meter (Agilent E4980A) in the frequency of 20 to 2 MHz. In the course of measuring, a magnetic field is applied perpendicular to sample surface. The dynamic behaviors of liquid crystal molecular under magnetic field are discussed. Under constant applied magnetic field, samples with different spacer thicknesses (9, and 98 μm, respectively) have different curvature elasticity therefore show different dynamic behaviors. Moreover, because of the Freedericks transition, the real part of permittivity (at lower frequency ranges) increases with increasing applied magnetic field. Additionally, magneto-relaxation times of two samples are determined and the results reveal that due to the molecular anisotropic, the different directions of optical indexes exhibit different transmittance characteristics. Also, the results of dielectric analysis are found to agree well with the optical measurements.

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