SUPPRESSION OF CRYSTALLIZATION IN THE BINARY-SYSTEM 1,2-PROPANEDIOL-DEUTERIUM OXIDE - COMPARISON WITH LIGHT-WATER AS SOLVENT

The solid-liquid phase diagram of the binary system D2O-1,2-propanedio l has been studied for concentrations up to 50% w/w. The homogeneous n ucleation was also analyzed using an emulsification technique within t he classical theory. The isothermal and non-isothermal crystallization s of ice were studied during warming for samples which vitrify during the initial cooling down below the glass transition. The thermal analy sis was performed using the Johnson-Mehl-Avrami model extended to non- isothermal conditions. Comparisons are made with previous results from the binary system H2O-1,2-propanediol. The suppression of crystalliza tion during cooling is similar for both binary systems for concentrati ons in %mole/mole. The differences between melting and devitrification temperatures are also similar. The results do not indicate major diff erences between the crystallization kinetics with H2O or with D2O. Cal culations of the kinetics parameters do, however, underline detailed d ifferences. The suppression of the nucleation of ice is steeper for th e D2O system than for the H2O system, even if the homogeneous nucleati on temperatures are higher with D2O than with H2O. Estimates of the so lid-liquid surface free energies are higher for the H2O solvent than f or the D2O solvent and decrease as the 1,2-propanediol concentration i ncreases. They cross over for a concentration close to 89% mole/mole s olvent. For the isothermal and non-isothermal crystallization, the det ermination of the Avrami exponent is similar for the two solvents, wit h values of between 2.5 and 2 for solute concentrations higher than 37 .5% w/w. However, D2O presents higher absolute activation energy value s than H2O. These variations confirm that the nucleation is better sup pressed and the crystal growth less suppressed by addition of 1,2-prop anediol in D2O solutions than in H2O solutions for dilute concentratio ns.