Ultrafast energy transfer in water-AOT reverse micelles
Ultrafast energy transfer in water-AOT reverse micelles
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DOI：
10.1021/jp0723158
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发表时间：
2007-12-27
影响因子：
3.3
通讯作者：
Wiersma, Douwe A.
中科院分区：
文献类型：
--
作者：
Cringus, Dan;Bakulin, Artem;Wiersma, Douwe A.
提出了几何受限环境中水的振动动力学的光谱研究。直径范围为 1 至 10 nm 的三元微乳液 H2O/AOT/正辛烷（AOT = 双-2-乙基己基磺基琥珀酸酯或气溶胶-OT）的反胶束被用作被软物质边界包围的纳米级水滴的模型系统。 H2O 的 OH 拉伸区域中的飞秒非线性红外光谱完全证实了核/壳模型，其中捕获的水分子划分为两个分子子系：块状水核和离子表面活性剂头基附近的水化层。这两种不同的水种类表现出不同的弛豫动力学，因为它们不交换振动能量。观察到的光谱时间超快响应表现出局部特征，表明空间限制影响了位于水-两亲物边界附近的大约一个分子层。封装水滴的核心在其光谱特性方面与液态水的体相相似，即，它不显示任何真正的限制效应，例如依赖于水滴尺寸的振动寿命或旋转相关时间。与本体水中不同，界面水分子之间或从水化壳到块状核之间没有发生 OH 伸缩量子的分子间转移，这表明 H2O/AOT 界面附近的氢键网络受到强烈破坏。
A spectroscopic investigation of the vibrational dynamics of water in a geometrically confined environment is presented. Reverse micelles of the ternary microemulsion H2O/AOT/n-octane (AOT = bis-2-ethylhexyl sulfosuccinate or aerosol-OT) with diameters ranging from 1 to 10 nm are used as a model system for nanoscopic water droplets surrounded by a soft-matter boundary. Femtosecond nonlinear infrared spectroscopy in the OH-stretching region of H2O fully confirms the core/shell model, in which the entrapped water molecules partition onto two molecular subensembles: a bulk-like water core and a hydration layer near the ionic surfactant headgroups. These two distinct water species display different relaxation kinetics, as they do not exchange vibrational energy. The observed spectrotemporal ultrafast response exhibits a local character, indicating that the spatial confinement influences approximately one molecular layer located near the water-amphiphile boundary. The core of the encapsulated water droplet is similar in its spectroscopic properties to the bulk phase of liquid water, i.e., it does not display any true confinement effects such as droplet-size-dependent vibrational lifetimes or rotational correlation times. Unlike in bulk water, no intermolecular transfer of OH-stretching quanta occurs among the interfacial water molecules or from the hydration shell to the bulk-like core, indicating that the hydrogen bond network near the H2O/AOT interface is strongly disrupted.