Nucleation Behavior From Solution Based On Metastable Zone Models

Metastability is a probe for understanding and controlling the nucleation behavior of a substance in a solution or molten state.Based on the study of the metastable state in the solution crystallization process,a series of studies on the solution nucleation behavior have been carried out based on the metastable zone model.Firstly,since there is no metastable zone model can obtain the nucleation solid-liquid interfacial tension and nucleation kinetics from the metastable zone data,we applied and simplified Sangwal's metestable zone theory.Unlike Sangwal's theory,in this simplified model,the nucleation parameters are independent of saturation temperature T₀ and nucleation temperature T₁.Therefore,by employing this theory,the pre-exponential factor and solid-liquid interfacial tension can be obtained through the metastable zone experiment for the first time.Subsequently,we determined the metastable zone of Eszopiclone in butyl acetate to verified the model proposed in this paper.Secondly,owing to the lack of nucleation theory to describe the effects of subcooling and crystallization temperature on nucleation probability and nucleation rate in small scale,in this contribution,by employing the Possion distribution combined with the regular solution theory in the CNT framework,we construct a new model to describe the relationship between ln 1/t_ind and(T₀/?T)²/(T₀-?T)at different specific probability.Then,we choose the urea aqueous solution as a benchmark system and verified this model successfully.Furthermore,we explore the effect of driven force and temperature on the nucleation rate and indicated thatthe nucleation rate does not always decreases with decreasing the driven force since the temperature will play more significant role in the nucleation rate in some cases.Subsequently,we are aiming at resolve the problem that in the process of cooling crystallization,the influence of driving force and temperature on nucleation kinetics could not be discussed separately.We choose L-histidine as a benchmark system to uncover the effect of driven force and nucleation temperature on the nucleation rate.Once again,we prove that the nucleation rate does not always increase with the increase of the driving force.Reduce the driving force and improve the temperature may be advantageous in reducing the tension of the solid-liquid interface and increasing the nucleation collision factor,which is beneficial to the nucleation event.Finally,this paper further explores the problem that how the cooling rate and saturation temperature regulate the molecular self-assembly pathway of different crystal forms and the concomitant nucleation region in the nucleation metastable state.We found that the nucleation of different crystal forms of gestodene in ethanol solution is mainly controlled by thermodynamics,but when the competition between thermodynamics and kinetics is in an equilibrium state,concomitant nucleation may occur at this time.More importantly,at a given cooling rate,using the metastable zone theoretical model developed in this contribution,we can accurately predict the temperature and metastable zone widths when concomitant nucleation occurs,and find that with the increase of the cooling rate,both the saturation temperature and the corresponding metastable zone corresponding to the concommitant nucleation increases.The above studies have not been reported in the literature.