Nucleation of butyl paraben in different solvents

The primary nucleation induction time of butyl paraben in pure solvents: acetone, ethyl acetate, methanol, ethanol, and propanol and in 70% and 90% ethanol aqueous mixtures has been determined. At each condition, about 100 experiments have been performed in 5 mL scale to capture the statistics of the nucleation process. The induction times at each condition show a wide variation. The data has been evaluated within the framework of the classical nucleation theory using several of the current approaches. Overall, the data obtained from the different methods of evaluation are surprisingly consistent. At comparable driving forces, nucleation is clearly fastest in acetone and slowest in propanol, with methanol, ethyl acetate, and ethanol in between. Adding water to the ethanol leads to a clear reduction in the nucleation rate. The solid-solution interfacial energy of butyl paraben in the different solvents decreases in the order: 70% ethanol > 90% ethanol > propanol > ethanol > ethyl acetate > methanol > acetone, which is surprisingly well-correlated to a decreasing solvent boiling point. It is shown that the same trend can be found for other systems in the literature. With the assumption that the stronger the bonding in the bulk phases, the higher the interfacial energy becomes, this observation is paralleled by the fact that a metastable polymorph has a lower interfacial energy than the stable form and that a solid compound with a higher melting point appears to have a higher solid-melt and solid-solution interfacial energy.