聚氧乙烯-聚氧丙烯-聚氧乙烯聚合物形成微胞之焓變化研究

A Study on the Enthalpy Change of Micellization of Pluronics

崔宏瑋(Hung-Wei Tsuei)

指導教授 ： 陳立仁

國立臺灣大學/工學院/化學工程學研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.00344

摘要

在本研究中，我們利用高敏感型微差掃瞄熱卡計，針對五種結構為聚乙烯氧基─聚丙烯氧基─聚乙烯氧基(Pluronic)的界面活性劑進行研究，隨著熱卡計溫度的上升，藉著觀察系統熱容量的變化，從而討論界面活性劑形成微胞時的各種相關變因。

當界面活性劑以少量溶於水中時，各分子間將會以單個分子為單位散布溶解於水中，在固定濃度的條件下，隨著溫度的上升，散布的界面活性劑將會在某個特定的溫度點開始大幅度的聚集在一起，此一溫度點被定義為臨界微胞溫度。在微胞化的同時，通常會伴隨著熱量的變化，對許多單純的界面活性劑而言，此一熱量變化常會和溫度呈負相關的趨勢。

在我們的實驗結果中，我們發現對低濃度的Pluronics而言，系統的焓變化的確與溫度有遞減的關係，然而隨著濃度的上升，焓變化與溫度的關係開始有偏低的現象，甚至出現隨著溫度有正相關的轉折情形，而對於較大的分子而言，這樣的轉折會在較低的濃度發生。

另外，我們也對在界面活性劑在高溫部份的相變化行為作討論，發現對於高親水性分子與高疏水性分子的相變化較為單純，而親疏水比例均衡者可擁有豐富的相變化行為。最後我們以恆溫滴定熱卡計所得的實驗結果與微差掃描熱卡計作比較，兩者的實驗結果有良好的一致性。

關鍵字

聚氧乙烯 ； 聚氧丙烯 ； 微胞 ； 焓 ； 熱卡計

並列摘要

In our experiment, we study the triblock copolymers of poly(ethylene oxide)- poly(propylene oxide)- poly (ethylene oxide) (Pluronics) using high sensitivity differential scanning calorimeter (HSDSC). With the temperature increases, we discussed the factors of micellization by measuring the heat capacity change of system along with the temperature.

When a small amount of surfactants dissolved in the water, the surfactant will be a monomer dispersed in solution. As the temperature increases, the separate monomers will aggregate at a characteristic temperature, which is denoted as critical micelle temperature. At the same time, it is accompanied with large enthalpy change during the micellization. For some surfactants with simple structure, the enthalpy change will decrease with increasing temperature.

In our research, we found that the enthalpy change decreases, as expected, with increasing temperature. However, the enthalpy change starts departing from the linear relationship at higher concentration range. More unusually, it has a positive relationship with temperature at this concentration range. And the transition of enthalpy tendency seems beginning at lower concentrations for larger molecules.

In addition, we also discussed the phase transition of Pluronics solution which occurred at higher temperatures. The transition is simple for the quite high or low PEO/PPO ratio molecules. But there is rich phase behavior for middle PEO/PPO ratio ones. Finally we compared the HSDSC data with the result from isothermal titration calorimeter, and good consistency between these two methods are obtained.

並列關鍵字

Pluronics ； micelle ； calorimeter ； DSC ； enthalpy

參考文獻

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