Abstract
In a previous work (J. Phys. Chem. B 2003, 107, 9837), we reported liquid-liquid-phase splitting at negative pressures in mixtures of H 2O + D2O + 3-methylpyridine (3-MP) at the limit of pure H2O as the solvent, thus extending for the first time the L-L phase diagrams to this metastable region. We showed that there is an intimate relation between pressure and solvent deuterium content. Isotopic substitution (H/D) in water provokes subtle entropic effects that, in turn, trigger a significant pressure shift, opening a pressure-wide miscibility window of as much as 1600 bar. Isotope effects are quantum in origin. Therefore, a model that is both pressure-dependent and considers quantization constitutes a necessary tool if one wishes to fully describe the p, T, x critical demixing in these systems. In the current work, the statistical-mechanical theory of isotope effects is combined with a compressible pressure-dependent model. This combination enabled us to predict successfully the overall L-L phase diagram via differences in the vibrational mode frequencies of water on its transfer from the pure state to that of dilution in 3-MP: each of the three librational modes undergo a calculated red-shift of -(250 ± 30) cm-1, while the overall internal frequencies contribution is estimated as a total +(400 ± 25) cm-1 blue-shift.
Original language | English |
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Pages (from-to) | 1377-1387 |
Number of pages | 11 |
Journal | Journal of Physical Chemistry B |
Volume | 110 |
Issue number | 3 |
DOIs | |
Publication status | Published - 26 Feb 2006 |
Keywords
- Binary mixtures
- Pyridine
- Excess molar