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  • 學位論文

皮秒脈衝串引致氯鋁酞青素-乙醇溶液之質量傳輸效應

Study of Mass Transport Induced by Picosecond Pulse Trains in Chloroaluminum Phthalocyanine-Ethanol Solution

指導教授 : 魏台輝
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摘要


19932000期間W. Kholer團隊逐步改善傳統熱擴散致被迫銳利散射實驗 (thermal diffusion forced Rayleigh scattering;TDFRS),並在其中加入外差探測功能 (optical heterodyne detection;OHD),使成為一修正版的TDFRS (以下稱OHD-TDFRS)。有別於傳統的TDFRS,OHD-TDFRS除可量測二元系統組成成份的索雷特係數 (Soret coefficients) 大小外,亦可決定其正負值。隨OHD-TDFRS的發展漸趨成熟,有關熱擴散與質量擴散的研究變得越來越活躍,許多二元系統 (譬如二元混合溶液、高分子溶液以及膠質粒子懸浮液等)的兩種擴散性質都透過此技術而被釐清,甚至這些二元系統組成成份的索雷特係數值也被精確地量測。這些實驗結果引領了熱擴散與質量擴散的微觀機制探討,目前分子動力學 (molecular dynamics;MD) 模擬方法是最能正確估計索雷特係數,但它仍未能完全解釋兩種擴散的微觀機制。基於此,相關的理論模型及數值模擬方法至今仍在蓬勃地發展中。值得注意的是,OHD-TDFRS所觀察到的熱擴散與質量擴散都屬準靜過程。 2004年起,本實驗室曾以時寬為19皮秒的脈衝為光源,以Z-scan技術探討氯鋁酞青素-乙醇 (二元系統)中溶質分子的質量傳輸效應。經12年研究,我們認為19皮秒的脈衝所造成的溶質分子質量傳輸效應是一種非準靜過程,超過熱擴散與質量擴散所能解釋。為進一步確定吾人的判斷,我們曾改用2.8奈秒的脈衝為光源,用Z-scan技術探討同樣溶液中的質量傳輸效應,實驗結果支持我們先前的判斷。 因為以上結果,我們接續思索當脈衝時寬介於2.8 奈秒與連續光源區間時,溶質分子的質量傳輸現象是否仍類似於19皮秒或2.8奈秒的實驗結果,屬於一種非準靜過程,或它較像是連續光源的實驗結果,屬於準靜過程。 本研究採用包跡時寬為13.8 ns (介於2.8奈秒與連續光的時寬之間)的皮秒脈衝串為激發光源,以Z-scan技術調查兩高低濃度 (6*10-4 M與1.7*10-4 M) 的氯鋁酞青素-乙醇溶液的質量傳輸現象,實驗結果顯示,皮秒脈衝串所引致的溶質遷移行為近似於19皮秒單脈衝為光源所造成的結果,同屬非準靜過程。

並列摘要


Since W. Kholer et al. embedded the optical heterodyne detection (OHD) system into the thermal diffusive forced Rayleigh scattering (TDFRS) technique in the 1990s, a new version of TDFRS, referred to as OHD-TDFRS, was established to measure the thermal and mass diffusion properties of various binary systems. With this technique, many reliable results of various binary systems, e.g., liquid mixtures, polymer solutions, colloidal suspensions, etc, have been first obtained. Remarkably, the sign change of the Soret coefficients STs with the mass fraction has been unprecedentedly observed in certain binary systems involving water as a constituent, e.g., poly (ethylene oxide) (PEO) in ethanol-water mixture, colloidal boehmite rods in ethanol-water mixture, ethanol-water and methanol-water solutions. To understand deeper the OHD-TDFRS results of binary small-molecule liquids at the molecular level, molecular dynamics (MD) simulation methods developed based on irreversible thermodynamics and non-equilibrium statistical mechanics have been used to compute STs to be compared with the ones obtained by quantitatively fitting the experimental results. However, a physical explanation of thermal diffusion at the molecular level is not yet clear yet up to date. When continuous wave (CW) laser light at moderate power has been commonly used to investigate thermal and mass diffusions, we have explored, since 2004, short pulse-induced solute migration in an ethanolic solution of chloroaluminum phthalocyanine, dubbed CAP-ethanol, using the Z-scan technique with 532 nm laser pulses with widths of 19 picosecond (ps) and 2.8 nanosecond (ns). As a result, by comparing the results obtained on both time scales, we have verified that 19 ps pulse-induced solute migration is a non-quasistatic process and more complicated than thermal diffusion can explain. In this thesis we investigate solute migration in CAP-ethanol using the Z-scan technique with trains of 19 ps laser pulses separated by 7.1 ns and enveloped by 13.8 ns (HW1/eM) Gaussian profiles. When the envelope width (13.8 ns) is greatly longer than the width of individual pulses (19 ps), we wonder if thermal diffusion will come into play. The aim of this work is to clarify the mechanism of photo-absorption-caused solute migration at the microscopic level.

參考文獻


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