Hydrostatic Pressure Reveals Bilayer Phase Behavior of Dioctadecyldimethylammonium Bromide and Chloride

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• 作者：Masaki Goto ; Yuka Ito ; Shunsuke Ishida ; Nobutake Tamai ; Hitoshi Matsuki ; Shoji Kaneshina
• 刊名：Langmuir
• 出版年：2011
• 出版时间：March 1, 2011
• 年：2011
• 卷：27
• 期：5
• 页码：1592-1598
• 全文大小：849K
• 年卷期：v.27,no.5(March 1, 2011)
• ISSN：1520-5827

文摘

Bilayer phase transitions of dioctadecyldimethylammonium bromide (2C₁₈Br) and chloride (2C₁₈Cl) were observed by differential scanning calorimetry and high-pressure light-transmittance measurements. The 2C₁₈Br bilayer membrane showed different kinds of transitions depending on preparation methods of samples under atmospheric pressure. Under certain conditions, the 2C₁₈Br bilayer underwent three kinds of transitions, the metastable transition from the metastable lamellar crystal (L_c(2)) phase to the metastable lamellar gel (L_尾) phase at 35.4 掳C, the metastable main transition from the metastable L_尾 phase to the metastable liquid crystalline (L_伪) phase at 44.5 掳C, and the stable transition from the stable lamellar crystal (L_c(1)) phase to the stable L_伪 phase at 52.8 掳C. On the contrary, the 2C₁₈Cl bilayer underwent two kinds of transitions, the stable transition from the stable L_c phase to the stable L_尾 phase at 19.7 掳C and the stable main transition from the stable L_尾 phase to the stable L_伪 phase at 39.9 掳C. The temperatures of the phase transitions of the 2C₁₈Br and 2C₁₈Cl bilayers were almost linearly elevated by applying pressure. It was found from the temperature (T)鈭抪ressure (p) phase diagram of the 2C₁₈Br bilayer that the T鈭?i>p curves for the main transition and the L_c(1)/L_伪 transition intersect at ca. 130 MPa because of the larger slope of the former transition curve. On the other hand, the T鈭?i>p phase diagram of the 2C₁₈Cl bilayer took a simple shape. The thermodynamic properties for the main transition of the 2C₁₈Br and 2C₁₈Cl bilayers were comparable to each other, whereas those for the L_c(1)/L_伪 transition of the 2C₁₈Br bilayer showed considerably high values, signifying that the L_c(1) phase of the 2C₁₈Br bilayer is extremely stable. These differences observed in both bilayers are attributable to the difference in interaction between a surfactant and its counterion.