Construction of a temperature controlled sample stage and the application on single molecule study liquid crystals

• Main Authors: Yu-Tzu Chuang, 莊育慈
• Other Authors: Jui-Hung Hsu
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/22960137964336952326

碩士 === 國立中山大學 === 材料科學研究所 === 94 === In this dissertation, we construct a temperature controlled sample stage that is compatible with high numerical aperture objective optical microscope, and perform single molecule experiments under the system. Mixing dilute fluorophore (CdSe/ZnS quantum dot, DiI, Rhodamine B) into the liquid crystal matrix (5CB), we monitor the fluorescence dynamics of the individual fluorophore at various temperature. Different from the thermodynamic states of conventional materials, those specific class of materials which we called “liquid crystals” are attracted for their existence of unique liquid crystal phase, which exhibits a solid-state like higher orientation ordering, and a liquid-state like liquidity. Probe individual fluorophore allows us to monitor the nanometer length scale local structural and dynamic heterogeneity in the solid, liquid crystal and liquid phases. The operating temperature of the platform covers more than 20 oC to 40 oC range with stability much better than 0.1 oC. Quantum dot in PMMA exhibits a clear on-off blinking behavior, and the single exponential fluorescence lifetime relaxation. While in the solid phase of the liquid crystal matrix, quantum dot exhibits similar behavior, which indicates the quantum dot is confined in the matrix. However, there exists slightly difference in decay lifetime. On the contrary, in the liquid crystalline phase as well as the liquid phase, quantum dot exhibits bi-exponential relaxation behavior. Besides a similar time scale relaxation dynamics, there exists additional fast decay behavior, which is from the feasible rotational rotation in the non-rigid matrix. In particular, the anisotropic decay dynamics in the liquid crystalline phase indicates the orientation preference of the liquid crystal molecules. Fluorescence Correlation Spectroscopy (FCS) provides the information of local dynamics of various time scales. FCS results exhibit an unclear transition that crossovers several decades in time scale, which indicates the highly heterogeneity of the liquid crystal. The results of DiI exhibits different rising time in the fluorescence lifetime measurement, which implies the forming of aggregation due to the limited solubility of the DiI molecules in the liquid crystal matrix. Results of Rhodamine B exhibit a clear rotational diffusion dynamics at ~ microsecond scale and the corresponding translational diffusion dynamics at ~ mini-second scale. Moreover, the transition time scale of translational diffusion exhibits a temperature dependence. At higher temperature, it shifts to a shorter time scale.