Cd2+-induced interfacial structural changes of Langmuir-Blodgett films of stearic acid on solid substrates: a sum frequency generation study.
Cd2+-induced interfacial structural changes of Langmuir-Blodgett films of stearic acid on solid substrates: a sum frequency generation study.
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DOI：
10.1021/la036008e
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发表时间：
2004-01
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影响因子：
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通讯作者：
S. Ye;H. Noda;T. Nishida;Shigeaki Morita;M. Osawa
中科院分区：
文献类型：
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作者：
S. Ye;H. Noda;T. Nishida;Shigeaki Morita;M. Osawa
本文用高表面灵敏的和频光谱技术研究了硬脂酸LB膜的分子结构及其在固体基底上的最外层的稳定性。在SFG光谱中观察到的峰主要归因于LB膜最外层的末端甲基。在空气中的SFG光谱几乎是相同的，并且与LB膜的奇偶性质和厚度（1 - 12）无关，表明偶数LB膜在穿过水亚相和空气之间的界面后改变了其表面结构，特别是当Cd2+阳离子包含在水亚相中时。此外，我们已经证明了第一次使用原位SFG测量，在LB双层的硬脂酸的亲水性基板上的界面分子结构显着改变浸泡在水亚相中含有Cd 2+阳离子，而这样的结构变化尚未观察到在水亚相中没有Cd 2+。这些结果清楚地表明，重组过程发生在表面上的硬脂酸双层诱导的Cd 2+阳离子。硬脂酸的羧酸酯头基之间的静电相互作用，通过Cd 2+阳离子似乎发挥了重要作用，在表面重组过程中，在空气中和溶液中。
The molecular structures and their stabilities at the outmost-layer of the Langmuir-Blodgett (LB) films of stearic acid on solid substrates have been investigated by a highly surface-sensitive spectroscopic technique, sum frequency generation (SFG), in air and in aqueous solution, using the combination of both normal and deuterated stearic acid. Peaks observed in the SFG spectra are mainly attributed to the terminal methyl group at the outmost layer of the LB films. The SFG spectra in air are virtually identical and are independent of the odd-even property and thickness (1-12) of the LB films, indicating that the even-numbered LB film changes its surface structure after passing through the interface between the water subphase and air, especially when the Cd2+ cation was included in the water subphase. Furthermore, we have demonstrated for the first time using in situ SFG measurement that the interfacial molecular structure at the LB bilayer of stearic acid on the hydrophilic substrates significantly change with immersion in the water subphase containing Cd2+ cation while such a structural change has not been observed in the water subphase without Cd2+. These results clearly indicate that a reorganization process takes place on the surface of the stearic acid bilayer induced by the Cd2+ cation. The electrostatic interaction between the carboxylate headgroup of stearic acid via the Cd2+ cation seems to play an important role in the surface reorganization process both in air and in solution.