Non-Isothermal Nucleation and Crystallization of 12-Hydroxystearic Acid in Vegetable Oils

The non-isothermal nucleation rate of a self-assembling fibrillar network of 12-hydroxystearic acid in canola oil was found to be inversely proportional to the undercooling time exposure of the system. Moreover, fiber growth kinetics could be adequately modeled using the Avrami equation. Both nucleation and fiber growth kinetics displayed two distinct regimes, above and below 5 degrees C/min. The abrupt change in the rate of nucleation, crystal growth rate constant, and the degree of branching at this cooling rate are related to whether the nucleation and crystal growth processes are governed by mass transfer or thermodynamics. At rapid cooling rates, above 5 degrees C/min, the driving force for both nucleation and crystal growth is the time-dependent chemical potential difference between the molten solid in solution and the crystallized solid (the degree of undercooling or supersaturation). At low cooling rates, however, the rate of crystallization is no longer determined by this dynamic chemical potential difference, but rather only limited by time. In the slow cooling regime, we show that there are no noncrystallographic mismatches which would lead to fiber branching. Using the models developed and adapted in this work, we could accurately predict the fiber length, rate of nucleation, rate of crystal growth, induction time of nucleation, and the degree of branching of a 12HSA SAFIN.