Deuterium Isotope Effect on Glass Transformation Temperatures of Aqueous Inorganic Solutions

Abstract

Determinations have been made on the effect of deuterium substitution on the glass transformation temperatures (Tg) evaluated for aqueous solutions of about 15 wt. % HCl and SO3 by differential thermal-analysis measurements. Complete substitution of D2O as the solvent shifts Tg from 128.1° to 131.8°K for the HCl solution and from 143.7° to 146.3°K for the SO3 solution. This shift is linear with extent of D2O substitution. If it is assumed that the potential-energy barriers to configurational changes in the supercooled liquid are not altered by deuterium substitution, the above shifts can be interpreted as consistent with the proposition that the configurational changes which are immobilized when the solutions are cooled through the glass transformation involve simply the translation of single H2O or D2O groups. On the above basis, translational frequencies around 200 cm—1 observed by Raman spectroscopy in water correspond to potential-energy barriers around 2000 cal/mole. This is in rough agreement with hydrogen-bond energies, which are around 3000 cal/mole. This identification of the barriers with hydrogen bonds provides a reasonable support for assuming the barriers insensitive to deuterium substitution.