Suzuki Akira, Yui Hiroharu
Department of Chemistry, Faculty of Science, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan.
Department of Chemistry, Faculty of Science, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan.
J Colloid Interface Sci. 2015 Apr 1;443:188-96. doi: 10.1016/j.jcis.2014.12.017. Epub 2014 Dec 13.
The confinement of water in organic self-assemblies with nanometer-sized pores is ubiquitous in nature. Water pools in sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelles have been intensively studied as a representative model of such confined water. However, the freezing and melting behavior of such water pools is poorly understood owing to their poor structural stability under phase transition. In the present work, the melting of iced water pools accompanied by a reconstruction of AOT reverse micelles was studied with infrared spectroscopy. For all AOT reverse micelles tested (Rw: 1.2-4.4 nm), a characteristic ice-water coexistence phase was observed during melting. The results provide experimental evidence of the previously proposed core-shell structure of the water pool. For larger frozen reverse micelles (Rw>2.3 nm), shifts of the υ(OH) bands were observed. The spectra of the shifted υ(OH) bands were similar to those for the melted water pools in the smaller micelles. The mechanism of the reconstruction of AOT reverse micelles from their frozen states and the corresponding transient changes in the local environments were also discussed.
水在具有纳米级孔隙的有机自组装体系中的受限现象在自然界中普遍存在。双（2-乙基己基）磺基琥珀酸钠（AOT）反胶束中的水池作为这种受限水的典型模型已得到深入研究。然而，由于这些水池在相变过程中结构稳定性较差，其冻结和熔化行为尚不清楚。在本工作中，利用红外光谱研究了伴随AOT反胶束重构的冰水共存池的熔化过程。对于所有测试的AOT反胶束（Rw：1.2 - 4.4 nm），在熔化过程中观察到了特征性的冰水共存相。这些结果为先前提出的水池核壳结构提供了实验证据。对于较大的冷冻反胶束（Rw > 2.3 nm），观察到了υ(OH)带的位移。位移后的υ(OH)带的光谱与较小胶束中熔化水池的光谱相似。还讨论了AOT反胶束从冷冻状态重构的机制以及局部环境中的相应瞬态变化。
