Phase Transitions and Critical Behaviour of Binary Liquid Mixtures
Compared to the simple one-component case, the phase behaviour of binary liquid mixtures shows an incredibly rich variety of phenomena. In this contribution we restrict ourselves to so-called binary symmetric mixtures, i.e. where like-particle interaction
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Preferential Solvation in Mixed Solvents X. Completely Miscible Aqueous Co-Solvent Binary Mixtures at 298.15 K Yizhak Marcus* Department of Inorganic and Analytical Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel Summary. The Kirkwood-Buff integrals for 18 completely miscible aqueous co-solvent binary mixtures have been recalculated from thermodynamic data, and the volume-corrected preferential solvation parameters derived from them are presented. Also presented are these latter quantities for 15 additional such mixtures, for which the volume correction has not been applied previously. The selfinteraction of the water, the mutual interaction of the water and the co-solvent, and the self-interaction of the co-solvent at infinite dilution derived from these integrals and parameters are then discussed. The systems studied include aqueous hydrogen peroxide, methanol, ethanol, 1- and 2-propanol, 2-methyl-2-propanol, 2,2,2-trifiuoroethanol, 1,1,1 ,3,3,3-hexafiuoro-2-propanol, ethane-1,2-diol, glycerol, 2-methoxyethanol (at 313 and 343 K), 2-ethoxyethanol, 2-butoxyethanol, 2-aminoethanol, Nmethyl- and N,N-dimethyl-2-aminoethanol, tetrahydrofuran, l,4-dioxane, acetone, formic, acetic, and propanoic acids, piperidine, pyridine, acetonitrile, formamide, N-methyl- and N,N-dimethylformamide, N-methylacetamide, N-methylpyrrolidin-2-one (at 303 K), hexamethy1 phosphoric triamide, dimethylsulfoxide, and tetramethylenesulfone (at 303 K). Keywords. Binary aqueous solvents; Preferential solvation; Kirkwood-Buff integrals.
Introduction A fairly large number of preferential solvation studies employed the Kirkwood-Buff integrals, G ij , Gij = 0
fXl (gij -
1 ) 471T 2 dr
(1)
where gij is the pair correlation function, denoting the probability of finding a molecule of species i in a volume element at the distance r from the center of a molecule of species j. The product Pi . Gij , where Pi is the number density of molecules of species i in the bulk of the mixture, represents the excess, if positive, or deficiency, if negative, of molecules of species i in the space around a given
*
E-mail: [email protected]
W. Linert (ed.), Highlights in Solute-Solvent Interactions © Springer-Verlag Wien 2002
y. Marcus
152
molecule of species j. An excess means attractive interactions between molecules of i and j, i.e. preferential mutual solvation, whereas a deficiency means that selfinteractions of i-i and j-j are preferred to mutual interactions. These integrals have been obtained for binary aqueous solvent mixtures (where in the following subscript W signifies water and subscript S the co-solvent; i and j represent any component) mainly from thermodynamic data [1-20] (where Ref. [20] constitutes Part 9 of this series), but also from structural fluctuation measurements [21, 22], and have been employed to describe preferential solvation. From thermodynamic data the integrals are calculated using the following expressIOns:
Gws Gww
=
RT("'T - VwVs/VD)
(2)
RT("'T + (xs/(1 - xs))(VVVD)) - V /(1 - xs)
(3)
Gss =
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