Effect of ions on phase diagrams of binary systems

Abstract

Phase diagrams, hydrogen bonding and molecular–ionic interactions have been studied by means of FTIR spectroscopy and theoretical decorated lattice (DL) approach. The modeling of the evolution of phase diagrams of two binary organic mixtures (2,6-lutidine–water, tetrahydrofuran–water) upon introduction of ions into solutions has been performed. The shifts of νOD bands of isotopically isolated HOD molecules in the first hydration shell of Cl^- with respect to their position in the bulk have been observed by approaching the critical conditions: 2505→2518 cm^-1 (2,6-lutidine–H₂O–KCl) and 2524→2518 cm^-1 (tetrahydrofuran–H₂O–KCl). The experimental data together with theoretical DL calculations lead to the conclusion that the two main factors stimulating the phase separation are the changes of the hydrogen bond energies in the first hydration sphere of anions and the appearance of new favorable molecular orientations. The possibility of manifestation of charge-density waves is discussed.