A Study on the Thermodynamic Properties of Micellization of Cationic Surfactants CnTAB
Date Issued
2004
Date
2004
Author(s)
Liao, Chao-Min
DOI
zh-TW
Abstract
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.
Subjects
恆溫滴定熱卡計
界面活性劑
微胞
surfactant
micelle
ITC
Type
thesis
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