Orientational dynamics of water confined on a nanometer length scale in reverse micelles.
Orientational dynamics of water confined on a nanometer length scale in reverse micelles.
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DOI：
10.1063/1.1883605
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发表时间：
2005-04
期刊：
影响因子：
--
通讯作者：
H. Tan;I. Piletic;M. Fayer
中科院分区：
文献类型：
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作者：
H. Tan;I. Piletic;M. Fayer
利用超快红外偏振和光谱分辨泵浦-探测光谱研究了在二（2-乙基己基）磺基琥珀酸钠（AOT）反胶束中，水溶液中稀溶液的OD羟基伸缩在纳米尺度上的时间分辨取向各向异性，并与本体水的实验结果进行了比较.三个水纳米池尺寸（4.0，2.4，和1.7 nm）的取向各向异性数据可以很好地拟合与双指数衰减。双指数衰减分析使用摆动在一个锥模型，涉及快速取向扩散锥内，然后较慢，充分的取向松弛。该数据提供了锥角、锥内运动的扩散常数以及作为纳米池尺寸的函数的最终扩散常数。这两个过程可以被解释为一个局部的OD角波动和一个全局的氢键网络重排过程。长和短指数衰减的相对振幅的趋势表明随着纳米池尺寸减小刚性增加。长衰减常数的趋势表明随着反胶束尺寸的减小，氢键网络重排时间更长。研究的反胶束的各向异性测量外推到约0.33，而不是理想值0.4，这表明初始惯性组件的存在下，在各向异性衰减太快，无法解决。非常快的衰减组件是一致的初始惯性取向运动，这是在AOT反胶束中的水发表的分子动力学模拟。确定惯性定向运动发生的角度。结果与分子动力学模拟结果半定量一致。
The time-resolved orientational anisotropies of the OD hydroxyl stretch of dilute HOD in H(2)O confined on a nanometer length scale in sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelles are studied using ultrafast infrared polarization and spectrally resolved pump-probe spectroscopy, and the results are compared to the same experiments on bulk water. The orientational anisotropy data for three water nanopool sizes (4.0, 2.4, and 1.7 nm) can be fitted well with biexponential decays. The biexponential decays are analyzed using a wobbling-in-a-cone model that involves fast orientational diffusion within a cone followed by slower, full orientational relaxation. The data provide the cone angles, the diffusion constants for motion within the cones, and the final diffusion constants as a function of the nanopool size. The two processes can be interpreted as a local angular fluctuation of the OD and a global hydrogen bond network rearrangement process. The trend in the relative amplitudes of the long and short exponential decays suggest an increasing rigidity as the nanopool size decreases. The trend in the long decay constants indicates a longer hydrogen bond network rearrangement time with decreasing reverse micelle size. The anisotropy measurements for the reverse micelles studied extrapolate to approximately 0.33 rather than the ideal value of 0.4, suggesting the presence of an initial inertial component in the anisotropy decay that is too fast to resolve. The very fast decay component is consistent with initial inertial orientational motion that is seen in published molecular-dynamics simulations of water in AOT reverse micelles. The angle over which the inertial orientational motion occurs is determined. The results are in semiquantitative agreement with the molecular-dynamics simulations.