Dynamic properties of confined hydration layers.
Dynamic properties of confined hydration layers.
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DOI：
10.1039/b805244a
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发表时间：
2009
影响因子：
3.4
通讯作者：
S. Perkin;R. Goldberg;Liraz Chai;N. Kampf;J. Klein
中科院分区：
文献类型：
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作者：
S. Perkin;R. Goldberg;Liraz Chai;N. Kampf;J. Klein
由于最近发现水和一价Na+水溶液在被限制在云母表面之间的几个分子层的膜中时保持流体状，[Raviv等人，Nature，2001，413，51-54;以及Raviv和Klein，Science，2002，297，1540-1543]，我们现在通过比较0.1M Na+、Cs+和Ni 2+盐溶液的剪切力和法向力性质来扩展先前的研究，这些溶液在约束下表现出不同范围的行为。在水合Na+的情况下，我们将先前的研究扩展到更高的压力，高达约10个大气压，并在这些高压下记录了水合层的类似流动性。已经发现在云母片之间限制下的含水Cs+膜不能支持施加的负载-也就是说它们没有表现出任何水合排斥状态-这是由于它们的较低水合能[参见Goldberg等人，物理化学化学物理学，2008，10，4939-4945]，这与Na+的性质形成鲜明对比。我们发现，0.1 M的Ni 2+溶液仍然接近其体积粘度下降到纳米薄膜，但没有表现出水合排斥。通过比较这一系列阳离子的性质，不同的化合价和水合作用，我们的目标是研究离子作为有效润滑剂的条件，我们称之为“水合润滑”机制。
Prompted by the recent discovery that water and aqueous monovalent Na+ solutions remain fluid-like when confined to films of a few molecular layers between mica surfaces,[Raviv et al., Nature, 2001, 413, 51-54; and Raviv and Klein, Science, 2002, 297, 1540-1543] we now extend the previous study by comparing the shear- and normal-force properties of 0.1 M Na+, Cs+ and Ni2+ salt solutions which demonstrate a diverse range of behaviours under confinement. In the case of hydrated Na+ we extend the previous study to higher pressures, up to approximately 10 atmospheres, and record similar fluidity of the hydration layers at these elevated pressures. Aqueous Cs+ films under confinement between mica sheets have been found to be unable to support an applied load--that is to say they do not demonstrate any hydration repulsion regime--as a result of their lower hydration energy [see Goldberg et al., Phys. Chem. Chem. Phys., 2008, 10, 4939-4945] which contrasts with the properties of Na+. We show that 0.1 M Ni2+ solution remains close to its bulk viscosity down to nanometre thin films, but does not demonstrate a hydration repulsion. By comparing the properties of this range of cations, with differing valency and hydration, we aim to examine the conditions under which ions serve as effective lubricants and what we call the 'hydration lubrication' mechanism.