Structural, single-particle and pair dynamical properties of acetone–chloroform mixtures with dissolved solutes

Generalized Form for Finite-Size Corrections in Mutual Diffusion Coefficients of Multicomponent Mixtures Obtained from Equilibrium Molecular Dynamics Simulation

The system-size dependence of computed mutual diffusion coefficients of multicomponent mixtures is investigated, and a generalized correction term is derived. The generalized finite-size correction term was validated for the ternary molecular mixture chloroform/acetone/methanol as well as 28 ternary LJ systems. It is shown that only the diagonal elements of the Fick matrix show system-size dependency. The finite-size effects of these elements can be corrected by adding the term derived by Yeh and Hummer (J. Phys. Chem. B2004, 108, 15873–15879). By performing an eigenvalue analysis of the finite-size effects of the matrix of Fick diffusivities we show that the eigenvector matrix of Fick diffusivities does not depend on the size of the simulation box. Only eigenvalues, which describe the speed of diffusion, depend on the size of the system. An analytic relation for finite-size effects of the matrix of Maxwell–Stefan diffusivities was developed. All Maxwell–Stefan diffusivities depend on the system size, and the required correction depends on the matrix of thermodynamic factors.

Experiments on tracer diffusion in aqueous and non-aqueous solvent combinations

Forced Rayleigh scattering is used to study the tracer diffusion of an azobenzene in binary combinations of polar solvents, including water. In the absence of water, the tracer diffusion coefficient D in the mixture lies between the diffusion coefficients within the pure solvents, on a curve that is reasonably close to the prediction of free-volume theory. If water is present, on the other hand, the diffusion coefficient displays a minimum that is less than the smaller of the two pure-solvent values. We attempt to understand the different behavior in water by concentrating on the fairly hydrophobic nature of the solute, leading to a first solvent shell that is hydrophobic on the inside and hydrophilic on the outside. We also believe that clusters of amphiphiles explain the observation that, in aqueous combinations, D is nearly constant above a certain amphiphile mole fraction.