Determination of nucleation kinetics from the induction time of 1,1-diamino-2,2-dinitroethylene (FOX-7) in DMSO/Water

Abstract

Elucidation of the crystal nucleation process can provide guidance for controlling crystal size and quality. To understand the nucleation process of 1,1-diamino-2,2-dinitroethylene (FOX-7), the induction time and nucleation kinetics of FOX-7 were studied using a turbidity method in a binary solvent system (DMSO ​+ ​water, xDMSO ​= ​0.3364) under cooling crystallization conditions. Using the CrystalSCAN system, the induction time was determined at a range of temperatures (325.05, 335.25, 343.15, 348.15, and 354.65 ​K) and supersaturations (S) (1.20, 1.22, 1.24, 1.27, 1.30, 1.32, 1.35, 1.37), and it was found that induction time decreases as supersaturation increases. The system displayed a homogeneous nucleation mechanism at high supersaturation ratios (≥1.27) and heterogeneous nucleation at low supersaturation ratios, below 1.25. The FOX-7 crystal exhibited a continuous growth mechanism, as inferred from the value of the surface entropy factor (f). The induction time data were analyzed using the classical nucleation theory to calculate the interfacial energy (γ) and various nucleation parameters, including the radius of the critical nucleus (r∗), critical free energy of the nucleus (ΔG∗), molecular number of the critical nucleus (i∗), and the nucleation rate (J). The morphology of FOX-7 crystals changed negligibly with varying temperature and supersaturation, while the average particle size decreased with an increase in supersaturation and a decrease in temperature.