Prediction of velocity cross-correlation coefficients of binary liquid mixtures

Abstract

Velocity cross-correlation coefficients (VCC's) may be used as measures of the coupling between the velocities of different molecules in binary liquid mixtures. The hydrodynamic expression for the VCC's proposed by Friedman and Mills is used to derive expressions for the VCC's in terms of molecular diameters and the Kirkwood-Buff parameters. The main approximation is the use of the Ornstein-Zemike form for the liquid radial distribution functions supplemented by a small separation cutoff. An ideal reference system for the VCC's is proposed in terms of hypothetical ideal Kirkwood-Buff parameters. Experimental VCC's, experimental Kirkwood-Buff parameters, theoretical VCC's using our expression, and reference VCC's are computed from literature data for eight binary liquid systems ranging from nearly thermodynamically ideal to very nonideal. Good agreement is shown between the experimental and predicted VCC's over the entire composition range of these mixtures.

Computer simulation study of the dynamic cross-correlations in liquids

“…SO in MD simulations of binary mixtures it is sufficient to calculate only three independent velocity tcf's since the other ones may be calculated by using equations (13) and (14). Similar relations may be obtained for the mean molecular displacement correlation functions and diffusion coefficients.…”

“…We evaluated Z~(t), Zd(t) and Z~(t) (a ~ b) from the velocities in MD simulations using expressions (4) and (1). The other velocity tcf's were obtained with equations (13) and (14). The same procedure was used to obtain the mean molecular Downloaded by [McGill University Library] at 09:07 05 January 2015 displacements.…”

“…Recently, the D~ coefficients have been the subject of several experimental [8][9][10][11] and theoretical [2,3,[12][13][14] analyses. Although they are in general dependent on the hydrodynamic interactions, in the case of electrolyte solutions they were used for testing the reliability of the ion-ion solvent averaged models [12,15,16].…”

Distinct Diffusion in Macromolecule‐Solvent Mixtures

“…Particularly, an approach based on the use of KirkwoodBuff (KB) integrals, [10] a second one based on a hydrodynamic approximation, due to Friedman and Mills (FM), [4] and a third one [6] based on Hartley-Crank equation (HC) will be considered. All these standards refer to ideal systems, as the Hertz's standard does in the velocity correlation analysis, treated in a previous paper.…”

“…The approximated Equation (8) is considered as a baseline for non-ideal systems, and it was previously tested for a wide range of non-ionic binary mixtures. [4] The KB-based D d i0 , in a baricentric reference frame, for a non-ionic system, is [4,10] …”