Concentration fluctuations in fluid mixtures

摘要

The B matrix of the Kirkwood-Buff theory of solutions describes number fluctuations of the component species. We show how, when the eigenvalues of the B matrix are widely different in magnitude, the description of the fluctuations can be simplified by restriction to a lower dimensional subspace of composition space. This simplification entails a loss of accuracy, which is argued to be often acceptable. The development is illustrated by application to water-urea and water -2,2,2 trifluoroethanol solutions. It is concluded that in these cases, the fluctuations of the components are coupled primarily by keeping the amount of void space in the solution almost constant. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2992130]