Thermodynamic Theory and Dynamic Light Scattering Studies of Mixed Short-Chain Lecithin Micelles
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- 作者：Tsang-Lang Lin ; Yuan Hu ; and Wen-Jiun Liu
- 刊名：Langmuir
- 出版年：1997
- 出版时间：March 19, 1997
- 年：1997
- 卷：13
- 期：6
- 页码：1422 - 1429
- 全文大小：281K
- 年卷期：v.13,no.6(March 19, 1997)
- ISSN：1520-5827
文摘
In this study, we develop a thermodynamic theory for ideally mixedrodlike micelles. The rodlike micelleis modeled as consisting of two end caps and one cylindrical middlesection. A linear model for the endcaps' composition is also proposed to determine how the end caps'composition varies with the end caps'size. Also, the thermodyanmic theory is applied to study mixedmicelles formed by dihexanoylphosphatidylcholine (diC6PC) anddiheptanoylphosphatidylcholine (diC7PC). Thehydrodynamic radius of themixed micelles is measured by dynamic light scattering for mixeddiC6PC and diC7PC micelles at atotalconcentration of 25 mM but with various mixing ratios. Themeasured hydrodynamic radii of the mixedmicelles are in good agreement with the values computed according tothe thermodynamic theory. Boththe theoretical and experimental results demonstrate that the mixedmicelles' mean size initially increasesslowly with an increasing percentage of diC7PCconcentration in the solution. Next, the mixedmicellesgrow rapidly when the percentage of diC7PCconcentration exceeds about 50%. Detailed analyses ofthemixed micelles by the thermodynamic theory indicate that thecylindrical section of the rodlike micelleson average contains only a few (around five) diC6PCmolecules for all mixing ratios; meanwhile the numberof diC7PC molecules in the cylindrical sectionsteadily increases as the percentage of diC7PC in thesolutionincreases. The average number of diC6PC moleculesper micelle in its end caps decreases with an increasingpercentage of diC7PC in the solution, while theaverage number of diC7PC molecules per micelle in itsendcaps increases. Moreover, the end caps' average size steadilyincreases with an increasing concentrationpercentage of diC7PC.