Structure and dynamics of reverse micelles containing supercooled water investigated by neutron scattering.
Structure and dynamics of reverse micelles containing supercooled water investigated by neutron scattering.
复制标题
通过中子散射研究含有过冷水的反胶束的结构和动力学。
DOI：
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
B. Stühn
中科院分区：
文献类型：
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作者：
T. Spehr;B. Frick;I. Grillo;P. Falus;M. Müller;B. Stühn
我们对微乳液液滴在低温下的结构、形状起伏和平移扩散进行了详细的中子散射研究。我们研究了三元微乳液D2O、AOT[二(2-乙基己基)琥珀酸单酯]和甲苯-D8(或庚烷-D16)，它们在室温附近形成球形水滴，被分散在油中的一层AOT包围。在T=290K，水与AOT的摩尔比omega在3到12之间变化时，我们发现使用小角中子散射的水核半径Rc分别在7到18 A之间。我们在T=220K的低温下对该结构进行了表征。冷却后，液滴结构保持不变，R_{c}保持大致恒定，直到承压水深度过冷的温度。在依赖于欧米伽的温度T_{S}下，我们观察到所有成分的液滴都有收缩，这取决于初始液滴的大小：初始半径越小，T_{S}越低。在研究的最低温度T=220K下，我们发现一个不依赖于欧米伽的剩余水核心，对应于每个AOT分子中大约有2个水分子。用中子自旋回波谱监测了一个微乳液(omega=8，R_(W)=12 A)从T=300K到相应收缩温度T_(S)以下的形状涨落和平移扩散。从而确定在整个研究的温度范围内，液滴稳定的弯曲弹性为kappa=0.3kB}T。从这些结果中，我们不能确定表面活性剂膜弹性和液滴的低温结构不稳定性之间的联系。此外，我们的结果表明，反向AOT胶束是研究软承压水的一个很好的工具，可以在很大的限制尺寸和温度范围内一直到过冷态。
We present a detailed neutron scattering study of the structure, shape fluctuations, and translational diffusion of microemulsion droplets at low temperatures. We investigate the ternary microemulsion D2O , AOT [bis(2-ethyl-hexyl) sulfosuccinate], and toluene-d8 (or heptane-d16) which forms spherical water droplets surrounded by a monolayer of AOT dispersed in oil around room temperature. At T=290 K , varying the molar ratio omega of water to AOT between 3 and 12, we find using small angle neutron scattering water core radii R_{c} between 7 and 18 A , respectively. We characterize the structure at low temperatures down to T=220 K . Upon cooling the droplet structure is maintained and R_{c} stays roughly constant down to temperatures where the confined water is deeply supercooled. At an omega -dependent temperature T_{s} we observe for all compositions a shrinking of the droplets, which depends on the initial droplet size: the smaller the initial radii, the lower the T_{s} is. At the lowest investigated temperature T=220 K we find an omega -independent remaining water core corresponding to a number of about 2 water molecules per AOT molecule. Neutron spin-echo spectroscopy is used to monitor shape fluctuations and translational diffusion for one microemulsion ( omega=8 , R_{w}=12 A ) from T=300 K down to temperatures below the corresponding shrinking temperature T_{s} . Thereby we determine the bending elasticity to be kappa=0.3k_{B}T over the whole investigated temperature range where the droplets are stable. From these results we cannot establish a link between surfactant membrane elasticity and low temperature structural instability of the droplets. Moreover, our results show that reverse AOT micelles are an excellent tool for the study of soft confined water over a broad range of confining sizes and temperatures down to the supercooled state.