Insights into the Role of Solvents in Nucleation Kinetics of Glutaric Acid from Metastable Zone Widths

Nucleation of zeolitic imidazolate frameworks: from molecules to nanoparticles

We have studied the clusters involved in the initial stages of nucleation of Zeolitic Imidazolate Frameworks, employing a wide range of computational techniques. In the pre-nucleating solution, the prevalent cluster is the ZnIm₄ cluster (formed by a zinc cation, Zn²⁺, and four imidazolate anions, Im^-), although clusters such as ZnIm₃, Zn₂Im₇, Zn₂Im₇, Zn₃Im₉, Zn₃Im₁₀, or Zn₄Im₁₂ have energies that are not much higher, so they would also be present in solution at appreciable quantities. All these species, except ZnIm₃, have a tetrahedrally coordinated Zn²⁺ cation. Small Zn_xIm_y clusters are less stable than the ZnIm₄ cluster. The first cluster that is found to be more stable than ZnIm₄ is the Zn₄₁Im₈₈ cluster, which is a disordered cluster with glassy structure. Bulk-like clusters do not begin to be more stable than glassy clusters until much larger sizes, since the larger cluster we have studied (Zn₁₄₄Im₂₈₈) is still less stable than the glassy Zn₄₁Im₈₈ cluster, suggesting that Ostwald's rule (the less stable polymorph crystallizes first) could be fulfilled, not for kinetic, but for thermodynamic reasons. Our results suggest that the first clusters formed in the nucleation process would be glassy clusters, which then undergo transformation to any of the various crystal structures possible, depending on the kinetic routes provided by the synthesis conditions. Our study helps elucidate the way in which the various species present in solution interact, leading to nucleation and crystal growth.

Insight into the Nucleation Mechanism of p-Methoxybenzoic Acid in Ethanol-Water System from Metastable Zone Width

The metastable zone width (MSZW) of p-methoxybenzoic acid (PMBA) in an ethanol-water system was measured using the polythermal method. The nucleation order m obtained by the Nývlt’s model indicates the nucleation of PMBA following a progressive nucleation mechanism at low saturation temperature (m = 3.18–7.50) and an instantaneous nucleation mechanism at high saturation temperature (m = 1.46–2.55). Then, combined with the metastable zone experiment and the Sangwal model, we found that the MSZW and the interfacial energy reached the maximum when the mass fraction of ethanol was 0.8, which resulted in the smallest crystal product size. Meanwhile, the maximum rcrit and ΔGcrit obtained based on the modified Sangwal model indicating the PMBA needs to overcome a higher nucleation barrier in the ethanol mass fraction of 0.8. Finally, we proposed a preferential strategy for adjusting MSZW by correlating the interfacial energy with the change in ethanol mass fraction, saturation temperature, and cooling rate, respectively.

Nucleation Behaviors of Adipic Acid in Different Polarity Solvent Based on Metastable Zone Width

In this contribution, we experimentally determined the metastable zone width (MSZW) of adipic acid (AA) in different polar solvents to reveal the nucleation behavior. We performed analyses for different cooling rates, saturation temperatures and polar solvents. The findings showed that the MSZW increased as the cooling rate increased, or saturation temperature or polarity decreased. Here, we suggest that the hydrogen bond donor capacity decreases as the polarity of the solvent decreases, which weakens the solute and solvent interaction and makes the desolvation process more difficult during nucleation. Furthermore, we found that the MSZW is mainly determined by the cooling rate, when the cooling rate is large enough. On account of the classical nucleation theory, it was found that the sizes of the critical nucleus and Gibbs nucleation energy do not increase monotonously with increasing driving force. Moreover, this study confirms that solid–liquid interface tension is associated with crystallization driving force.

Insight into the role of hydrochloric acid in the thermodynamics and nucleation kinetics behavior of Arbidol hydrochloride monohydrate from metastable zone widths

Contributions of hydrochloric acid to thermodynamics and nucleation kinetics of AHM were revealed by metastable zone width and modified Sangwal's theory, implying the nucleation rate monotonously increases with increment of hydrochloric acid.