A Study on the Thermodynamic Properties of Micellization of Surfactants
Date Issued
2005
Date
2005
Author(s)
Yen, Ling-Yao
DOI
zh-TW
Abstract
Surfactant is usually an organic molecule with a long hydrocarbon-chain. A surfactant molecule is composed of a polar hydrophilic group and a non-polar hydrophobic group. When the surfactant concentration reaches its “critical micellization concentration (cmc)”, surfactant molecules tend to aggregate and form micelles. During micelle formation, some apparent properties of surfactant solution would change, such as conductivity, enthalpy, etc.
In this thesis, the “Isothermal Titration Calorimeter(ITC)” is applied to measure the enthalpy change of micelle formation, ΔHm, and cmc for three nonionic surfactants: C8E5, C8E4, C8E3, and two ionic surfactants: sodium decyl sulfate (SDeS), sodium dodecyl sulfate (SDS).
The empirical temperature range of CiEjs and sodium alkyl sulfate are set between 15~40℃ and 20~70℃, respectively. The ΔHm and ΔCP can be evaluated from empirical cmc data via thermodynamic relationship. It is found that the calorimetric measurement provides more reliable information about ΔHm and ΔCP than those calculated from cmc. Moreover, experiment result shows the micellization process follows linear relationship of enthalpy-entropy compensation.
A special case must be taken with notice for the measurement of non-ionic surfactants. Especially, for surfactants with a small of ethylene oxide group or with a long hydrocarbon chain, the cloud point of short-chain CiEj, (such as C8E5, C8E4, C8E3) would appear at around ambient temperature. Phase separation might happen during experiment for some surfactants (C8E5, C8E4). To improve the empirical reliability of experiment data of pure CiEj and diluted CiEj (C8E5, C8E4) have to be combined for further analyses. Consequently, such a method can dramatically enhance the quality of experimental data.
Subjects
界面活性劑
微胞化
焓熵補償現象
微胞焓
surfactant
micelle
enthalpy-entropy compensation phenomenon
heat of micellization
Type
thesis