A simple DTA method of determining the glass transition temperature, Tg, of a supercooled liquid using small samples under high pressure has been developed and applied to the study of several anhydrous ionic liquid binary systems, and salt + water systems. Values of the pressure dependence of Tg have been compared with those predicted (a) from the pressure dependence of electrical conductance and (b) from the changes of heat capacity and expansion coefficient observed at Tg by use of the quasi-thermodynamic relation dTg/dP = TgVgΔα/ΔCp. In the case of alkali acetate + water systems, Tg is almost independent of pressure, and, in the case of the composition LiOAc·10 H2O, dTg/dP is actually negative. This result, which implies a decrease in expansion coefficient on increase of temperature through the glass transition, is conceptually incompatible with a free volume interpretation of liquid relaxational properties.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry