伪-Gel Formation by Amino Acid-Based Gemini Surfactants
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- 作者：Kenichi Sakai ; Kiyomi Ohno ; Kazuyuki Nomura ; Takeshi Endo ; Kazutami Sakamoto ; Hideki Sakai ; Masahiko Abe
- 刊名：Langmuir
- 出版年：2014
- 出版时间：July 8, 2014
- 年：2014
- 卷：30
- 期：26
- 页码：7654-7659
- 全文大小：270K
- ISSN：1520-5827
文摘
Ternary mixtures being composed of surfactant, long-chain alcohol, and water sometimes form a highly viscous lamellar gel with a hexagonal packing arrangement of their crystalline hydrocarbon chains. This molecular assembly is called 鈥溛?crystalline phase鈥?or 鈥溛?gel鈥? In this study, we have characterized 伪-gels formed by the ternary mixtures of amino acid-based gemini surfactants, 1-hexadecanol (C16OH), and water. The surfactants used in this study were synthesized by reacting dodecanoylglutamic acid anhydride with alkyl diamines and abbreviated as 12-GsG-12 (s: the spacer chain length of 2, 5, and 8 methylene units). An amino acid-based monomeric surfactant, dodecanoylglutamic acid (12-Glu), was also used for comparison. At a fixed water concentration the melting point of the 伪-gel increased with increasing C16OH concentration, and then attained a saturation level at the critical mole ratio of 12-GsG-12/C16OH = 1/2 under the normalization by the number of hydrocarbon chains of the surfactants. This indicates that, to obtain the saturated 伪-gel, a lesser amount of C16OH is required for the gemini surfactants than for the monomeric one (the critical mole ratio of 12-Glu/C16OH = 1/3). Small- and wide-angle X-ray scattering measurements demonstrated an increase in the long-range d-spacing of the saturated 伪-gels in the order 12-Glu <12-G8G-12 < 12-G5G-12 < 12-G2G-12. In the three gemini surfactant systems, the decreased spacer chain length resulted in the increased maximum viscosity and elastic modulus of the saturated 伪-gels at a given water concentration. This is caused by the decreased amount of excess water being present outside the 伪-gel structure (or the increased amount of water incorporated between the surfactant鈥揳lcohol bilayers). To the best of our knowledge, this is the first report focusing on the formation of 伪-gel in gemini surfactant systems.