LOWER CRITICAL SOLUTION POINT IN AQUEOUS MIXTURES - ENHANCED WATER ACTIVITY

Some aspects of the lower critical solution point (LCSP) of binary aqueous mixtures have been studied by means of renormalization-group (RG) and decorated lattice (DL) methods. The fitting of symmetrized experimental and calculated coexistence curves has revealed the advantage of the DL method. A new theoretical approach-enhanced water activity, i.e. the activity of water being much higher than that of the second component, has been developed yielding satisfactory agreement with unsymmetrized experimental composition (in mole fractions)-vs.-temperature curves in the vicinity of LCSP. It has been shown that the lower critical concentration is determined by the coordination number of the primary lattice. Thus, the information about the structure of the solution is being lost by the symmetrization. It follows that the second component containing oxygen, i.e. atom with two lone-pairs of electrons, stabilizes the ice-like structure of the solution. In the case of components with nitrogen atoms (one lone-pair) the structures with the higher coordination numbers are realized.