Abbott Andrew P, Hope Eric G, Palmer Donna J
Chemistry Department, University of Leicester, Leicester, LE1 7RH, U.K.
J Phys Chem B. 2007 Jul 19;111(28):8114-8. doi: 10.1021/jp066620p. Epub 2007 Jun 26.
This study shows that solutes can impart significant structure to supercritical solutions, resulting in unexpectedly high solution viscosity at pressures close to the critical value. The viscosity passes through a minimum as the pressure is increased, and this is accounted for by a solvation of the solutes leading to a decrease in solute-solute interactions. At high pressure, the solution viscosity is similar to that of the pure solvent as solvent-solvent interactions dominate. The increase in relative viscosity is modeled using a modified Dole-Jones equation, and it is shown that the change in relative viscosity is related to the volume fraction occupied by the solute. A general model is presented for simple solutes whereby the viscosity of a supercritical solution can be calculated from the molecular volume of the solute and the viscosity of the pure fluid. The higher than expected viscosity observed at low pressures is used to explain the variation of reaction rate constant with pressure.
本研究表明，溶质可赋予超临界溶液显著的结构，导致在接近临界值的压力下溶液粘度意外地高。随着压力增加，粘度先经过一个最小值，这是由于溶质的溶剂化导致溶质 - 溶质相互作用减少所致。在高压下，由于溶剂 - 溶剂相互作用占主导，溶液粘度与纯溶剂相似。使用修正的多尔 - 琼斯方程对相对粘度的增加进行建模，结果表明相对粘度的变化与溶质所占的体积分数有关。针对简单溶质提出了一个通用模型，据此可根据溶质的分子体积和纯流体的粘度计算超临界溶液的粘度。在低压下观察到的高于预期的粘度被用于解释反应速率常数随压力的变化。
