Primary and Secondary Nucleation Threshold of Succinic Acid: From the Perspective of Dimensionless Solid–Liquid Interfacial Tension

This contribution aims to clarify the influence of solvent, solubility, cooling rate, and seed loading on the primary and secondary nucleation threshold (SNT) from the perspective of metastable zone width (MSZW). Interestingly, we find that the MSZWs of succinic acid tend to decrease with increasing solubility. Therefore, we define dimensionless interfacial tensions under different conditions to further analyze the relationship between solubility and the MSZWs, as well as their impact on nucleation ability. When the solvent is the same, the dimensionless interfacial tension decreases with increasing temperature, promoting nucleation and narrowing the MSZWs of primary nucleation. When the solvent is different, the dimensionless interfacial tension increases with decreasing solubility, hindering nucleation and widening the MSZWs of primary nucleation. Furthermore, by coupling classical nucleation theory (CNT) with a secondary nucleation empirical model, we find that there is a linear relationship between 1/(T_nucΔT²_max) and ln(R/T_nuc) at the same seed loading. More importantly, the theoretical seed loading for the elimination secondary nucleation threshold was calculated and validated. Subsequently, we conclude that the dimensionless solid–liquid interfacial tension decreases linearly with increasing seed loading, thus leading to a narrower SNT. Finally, inspired by the dimensionless interfacial tension, by defining the dimensionless Gibbs free energy of nucleation, we reveal that dimensionless Gibbs free energy decreases linearly with increasing seed loading, hence reducing the nucleation difficulty and decreasing the SNT, thereby providing new insights and ideas for achieving precise regulation and prediction of the SNT.