EFFECT OF PH ON THE ICE CRYSTALLIZATION IN AQUEOUS-SOLUTIONS OF 1,2-PROPANEDIOL, CONSEQUENCE FOR VITRIFICATION SOLUTIONS

The pH effect on ice crystallization kinetics is presented in aqueous solutions of 1,2-propanediol. Isothermal and non-isothermal calorimetr ic measurements are analyzed and compared between samples where H2O wa s replaced either by 1N HCl, 1N NaOH or .5 NaCl. The ice nucleus densi ty is calculated from direct cryomicroscopic observations. The Johnson -Avrami-Mehl (JMA) model is used to characterizing the isothermal crys tallization. Amounts of ice are recorded during cooling for comparison . The substitution of H2O by a salt solution decreases the nucleation rate and obviously lowers its thermal range. Activation energies for i ce crystal growth at constant molal salt concentrations are similar. T he ratio K-o/N-1/n where N is the nucleus density, K-o is the kinetic constant and n the Avrami exponent for the crystallization is also pre sented as representative of the crystal growth. At constant molality, basic solutions present the lowest nucleation rate and crystal growth. For cryopreservation by vitrification, the present results support th e notion for a better vitrification tendency and lower crystal growth for solution having an excess of OH-. The choice still remains for a l ess toxic physiological solution.