- 學位論文
界面活性劑形成微胞之熱力學性質探討
A Study on the Thermodynamic Properties of Micellization of Surfactants
摘要
界面活性劑為有機長碳鏈分子，具有極性的『親水基』與非極性長鏈烷類之『疏水基』，當界面活性劑濃度增加至臨界微胞濃度時，界面活性劑分子會產生聚集現象，形成微胞。當微胞化現象發生時，界面活性劑之物性將發生明顯的改變，如：導電度、熱焓量變化等。 本研究透過實驗，藉由恆溫滴定熱卡計(ITC)測量界面活性劑之焓變化ΔHm與臨界微胞濃度數值，研究聚醚類型的非離子型界面活性劑CH3(CH2)i-1(OCH2CH2)jOH，簡稱CiEj，C8E5、C8E4、C8E3短鏈烷基碳鏈與陰離子型界面活性劑，十烷基硫酸鈉、十二烷基硫酸鈉。 前者CiEj探討溫度範圍為15℃~40℃，後者烷基硫酸鈉溫度範圍為20℃~70℃。探討由理論計算所得到之ΔHm、ΔCP(heat capacity)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ΔHm是可行的，但欲獲得準確的ΔCP，仍須以熱卡計直接加以量測，而在焓熵補償方面，其焓熵值呈現極佳的線性關係，符合焓熵補償現象。 溫度對聚氧乙烯系列之非離子型界面活性劑之量測cmc實驗影響特別大，尤其是短鏈烷基碳鏈(C8E5、C8E4、C8E3)影響甚深，當乙烯氧基(ethylene oxide group)的個數愈少或烷基碳鏈愈長，其雲點(cloud point)愈低，C8E5、C8E4，在實驗過程與溶液配置上，需特別注意界面活性劑溶液是否會發生相分離現象。為增加數據的可靠度，將純的CiEj與稀釋之CiEj實驗數據疊合，進行數據分析，發現其具有明顯且高相關性之可疊合趨勢，例如：C8E5、C8E4。
並列摘要
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.