Core Freezing and Size Segregation in Surfactant Core鈥揝hell Micelles

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• 作者：Beatrice Plazzotta ; Jing Dai ; Manja A. Behrens ; Istv谩n Fur贸 ; Jan Skov Pedersen
• 刊名：Journal of Physical Chemistry B
• 出版年：2015
• 出版时间：August 20, 2015
• 年：2015
• 卷：119
• 期：33
• 页码：10798-10806
• 全文大小：448K
• ISSN：1520-5207

文摘

Nonionic surfactants containing poly(ethylene oxide) are chemically simple and biocompatible and form core鈥搒hell micelles at a wide range of conditions. For those reasons, they and their aggregates have been widely investigated. Recently, irregularities that were observed in the low-temperature behavior of surfactants of the kind [CH₃(CH₂)_nO(CH₂CH₂O)_mH], (abbreviated CnEm) were assigned to a freezing鈥搈elting phase transition in the micellar core. In this work we expand the focus from the case of single component systems to binary surfactant systems at temperatures between 1 and 15 掳C. By applying small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), and density measurements in pure C18E20 and C18E100 solutions and their mixtures, we show that core freezing/melting is also present in mixtures. Additionally, comparing SAXS data obtained from the mixture with those from the single components, it was possible to demonstrate that the phase transition leads to a reversible segregation of the surfactants from mixed micelles to distinct kinds of micelles of the two components.