Solubility and Nucleation of Methyl Stearate as a Function of Crystallization Environment

Crystallization studies of methyl stearate from supersaturated dodecane, kerosene, and toluene solutions reveal strong evidence that solvent choice influences solubility and nucleation behavior. Solute solubility is less than ideal with toluene, kerosene, and dodecane, respectively, exhibiting the closest behavior to ideality, the latter consistent with the highest solvation. Polythermal crystallization studies using the Kashchiev–Borissova–Hammond–Roberts (KBHR) model [Kashchiev et al. J. Phys. Chem. B 2010, 114, 5441; Kashchiev et al. J. Cryst. Growth 2010, 312, 698; Camacho et al. CrystEngComm 2014, 16, 974] reveal a progressive nucleation (PN) mechanism with crystallite interfacial tension (γ_eff) values between 0.94 and 1.55 mJ/m², between 1.21 and 1.91 mJ/m², and between 1.18 and 1.88 mJ/m² for dodecane, kerosene, and toluene, respectively. Nucleation rates at the critical undercooling lie between 4.56 × 10¹⁶ and 1.79 × 10¹⁷ nuclei/mL·s, with the highest rates associated with crystallization from kerosene solutions. Iso-supersaturation nucleation rates are the highest for dodecane ranging from 2.39 × 10¹⁷ to 3.63 × 10¹⁸ nuclei/mL·s. Nucleation in toluene appears to be hindered by its relatively higher interfacial tension, which is associated with nucleation rates about an order of magnitude less than those obtained for dodecane.