陽離子型界面活性劑-烷基三甲基溴化銨形成微胞之熱力學性質探討

A Study on the Thermodynamic Properties of Micellization of Cationic Surfactants CnTAB

廖昭敏(Chao-Min Liao)

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(2004年)

https://doi.org/10.6342/NTU.2004.00142

摘要

本研究中第一部份藉由恆溫滴定熱卡計，研究陽離子型界面活性劑，烷基三甲基溴化銨CnTAB(n=10,12,14,16)在溫度範圍15℃∼80℃之焓變化ΔH與臨界微胞濃度(cmc)數值。我們也探討由理論計算所得到之ΔH、ΔCp與直接由ITC實驗得到數值之比較。結果顯示以理論計算方式計算ΔH是可行的，但欲獲得準確的ΔCp，仍須以卡計直接加以量測。而在焓熵補償方面，CnTAB的焓熵值呈現極佳的線性關係，符合焓熵補償現象。

本研究中第二部份為利用恆溫滴定熱卡計，研究溫度範圍15℃∼40℃之C14TAB + ethanol效應，由實驗結果發現cmc值會先隨著乙醇濃度增加達到最低值，此時的乙醇莫耳分率為xmin，然後cmc值再隨著乙醇濃度增加而增加。此結果最主要是受到乙醇會與水形成螯合物而改變溶劑的結構所影響。在焓熵補償方面，我們也發現C14TAB + ethanol系統之焓熵值呈現極佳的線性關係，亦符合焓熵補償現象。

本研究中第三部份則是藉由質量作用模式(mass action model)模擬DSC實驗曲線，其中可調的參數包含微胞聚集數n以及ΔCp。我們成左獐甡壎XDSC實驗曲線，並且可以得到整個掃瞄溫度範圍之聚集數n與溫度的變化關係。

關鍵字

恆溫滴定熱卡計 ； 界面活性劑 ； 微胞

並列摘要

In this study, the Isothermal Titration Calorimetry was applied to determine the enthalpy change of micelle formation and critical micelle concentration(cmc) for four ionic surfactants, Alkyl Trimethyl Ammonium Bromide,CnTAB(n=10,12,14 and 16)in salt-free aqueous solutions in temperature range 15-80℃. By applying the thermodynamic relationship the ΔH and ΔCp can be evaluated from the experimental cmc data, as a comparison to direct measurement result of ITC. It is found that the calorimetric measurements provide more reliable information about enthalpy and heat capacity accompanying micelle formation. The experiment result shows the micellization process follows the linear behavior of enthalpy-entropy compensation phenomenon.

In the second part of this research, the effect of the addition of ethanol on the micellization of C14TAB was studied also by ITC at temperatures of 15-40℃. The results show that with increasing ethanol concentration the cmc values first reach a minimum at an intermediate ethanol mole fraction xmin and then increase with increasing ethanol mole fraction. The results support the assumption that the dominant mechanism by which ethanol affects the micellization process is through its effect on the structure of water. And the results show that the C14TAB + ethanol systems also follow the linear behavior of enthalpy-entropy compensation phenomenon.

In the third part of this research, the Differential Scanning Calorimetry (DSC) curves were calculated using a mass-action model. The adjustable parameters are the aggregation number n and the heat capacity change ΔCp. The results show that it is successful to simulate DSC experiments curves and we can determine the variation of aggregation number n as a function of temperature.

並列關鍵字

surfactant ； micelle ； ITC

參考文獻

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