VITRIFIED DILUTE AQUEOUS-SOLUTIONS .4. EFFECTS OF ELECTROLYTES AND POLYHYDRIC ALCOHOLS ON THE GLASS-TRANSITION FEATURES OF HYPERQUENCHED AQUEOUS-SOLUTIONS

Aqueous solutions of LiBr, LiI, NaCl, NaI, KBr, CsCl, MgCl2, tetra-n-butylammonium bromide, propylene glycol, and glycerol (0.2-7 mol %) have been vitrified by hyperquenching, and their glass-liquid transition temperatures (T(g)) have been measured by differential scanning calorimetry. All solutions show similar patterns in their T(g) and increase in the heat capacity at T(g). T(g) decreases on the initial addition of the solute, reaches a minimum value, and then increases. The concentration at the T(g) minimum is characteristic of the solute. The first effect of solutes, which lowers T(g), is weakening of the H-bonded network, and the second, which raises T(g), is related to the hydration of ions, stability of ion pairs, H bonding with solutes, hydrophobic interactions, etc. The two dominate at different concentrations, and their compensation at a certain concentration produces the minimum. This occurrence is sufficiently general to conclude that explanations for the behavior of aqueous solutions should be sought in the changes in the nature of interactions between the water molecules and the solutes on hyperquenching, as the density of water decreases on cooling toward vitrification (the expansion coefficient of water is negative in the supercooled state) and not in the specific details of ionic charge, size, and molecular shapes.