Mechanistic Study on the Effect of Magnetic Field on the Crystallization of Organic Small Molecules

Exploring the effect of magnetic field on crystallization process and revealing the mechanism of magnetic field can enrich the regulation and intensification methods of crystallization process. In this paper, the effect of magnetic field on crystal nucleation and growth and its mechanism were comprehensively studied from the perspective of crystallization thermodynamics and kinetics, using a small organic molecule polyamide 56 salt as the model compound. The solubility, nucleation kinetics, and growth kinetics of the polyamide 56 salt were measured in the absence and presence of magnetic field, respectively. It was found that the magnetic field can improve the solubility of the model compound. The introduction of magnetic field can result in solubilization effect and enhance the directional motion of particles which can weaken the solute–solvent interaction. In addition, the introduction of magnetic field will prolong the nucleation induction period, widen the metastable zone width, and increase the nuclear barrier, which is the result of the competition between the directional motion of particles induced by the magnetic field and the inherent random Brownian motion. Moreover, the magnetic field can also effectively affect the crystal morphology and particle size, which is the result of the synergistic effect of nucleation kinetics and growth kinetics.