Apparent Molar Volumes and Solvation Coefficients in Ternary-pseudo-binary Mixtures [(Styrene+Ethyl Acetate or Benzene)+(N-Methyl-2-pyrrolidone+Ethyl Acetate or Benzene)]

Over the full range of compositions, in the ternary-pseudo-binary mixtures of x[（1-y）C6H5CH=CH2＋ yCH3COOC2H5（or C6H6）]＋（1-x）[（1-y）NMP＋yCH3COOC2Hs（or C6H6）], the apparent molar volumes of each pseudo-pure component at different y values were calculated from the density data at 298.15 K and atmospheric pressure. The results show that the four parameters cubic polynomial can correlate the apparent molar volume with the molar fraction well over the full molar fraction range. The limiting partial molar volumes and the molar volumes of each pseudo-pure component were evaluated with different methods. Based on the limiting partial molar volume and molar volume at a certain y value, a new universal coefficient termed as solvation coefficient γ was defined to describe quantitatively the solvation degree of pseudo-pure solute and the interactions of solute-solvent molecules from the macroscopical thermodynamics viewpoint. The results demonstrate the solvation coefficients decrease with the amount of the third component increasing for each pseudo-pure solute, irrespective of the pseudo-pure solvent. Then the solvation degrees of each pseudo-pure component, the specific interactions between the solute molecule and the solvent one were discussed in terms of the solvation coefficient.