The kinetics of the solidification of highly supersaturated solutions of palmitic acid in oleic acid: a comparison between two models

The crystallization of fatty acids is very important in industrial applications and biological systems. A comparison between theoretical models and experimental data helps in clarifying mechanistic aspects of these systems. In this contribution, we compare the performance of two models in fitting data from the crystallization of supersaturated solutions of palmitic acid in oleic acid. One of the models was developed by Avrami and the other is based on considering diffusion as limiting (the D-model). The D-model fitted the data better than the Avrami model in all cases. The D-model has a low value of the regression coefficient (r2, lower than 0.9) in only three cases. For these points, the thermodynamic force was smaller. Differences in the parameter n (an index of dimensionality) were observed; these differences indicate that clusters were present previous to the crystallization process. Furthermore, there appears to be a difference in the mechanism of crystallization of pure solutions of palmitic acid and solutions with a small fraction of oleic acid. Thus, one is lead to the conclusion that the rate of crystallization of fatty acids at high concentrations is limited by diffusion.