Perkin, S and Goldberg, R and Chai, L and Kampf, N and Klein, J (2009) Dynamic properties of confined hydration layers. FARADAY DISCUSS , 141 399 - 413. 10.1039/b805244a.
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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 behaviors under confinement. In the case of hydrated Na+ we extend the previous study to higher pressures, up to similar to 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 a effective lubricants and what we call the 'hydration lubrication' mechanism.
|Title:||Dynamic properties of confined hydration layers|
|Keywords:||AQUEOUS-ELECTROLYTE SOLUTIONS, ATOMIC-FORCE MICROSCOPE, MOLECULARLY THIN-FILMS, MICA SURFACES, SUBNANOMETER FILMS, CHLORIDE SOLUTIONS, CHARGED SURFACES, WATER, LIQUID, IONS|
|UCL classification:||UCL > School of BEAMS > Faculty of Maths and Physical Sciences > Chemistry|
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