Nucleation behavior of ethyl vanillin: Balance between chemical potential difference and saturation temperature

The experimental metastable zone widths (MSZWs) of ethyl vanillin (EVA) in ethanol, n-propanol, and n-butanol were measured by the polythermal method to describe the nucleation behavior of its unseeded cooling crystallization. In the framework of the classical nucleation theory (CNT), the effects of saturation temperature T0 and cooling rate R on MSZWs were mainly investigated by employing the modified Sangwal's theory to derive the pre-exponential factor A and the interfacial energy γ. It was found that when T0 decreases or R increases (resulting in a lower nucleation temperature), the value of γ increases proportionally, whereas the value of A changes slightly, which is largely determined by the type of solvent. Thus, the MSZWs in the given solvents are dominated by the change in the thermodynamic term γ. At lower T0, a large chemical driving force ∆μ is required to induce the nucleation event owing to the higher value of γ, which means that the solute molecules should pay more of a penalty to create the crystallite surface. Thus, the results indicate that the occurrence of nucleation depends on the balance between the chemical driving force ∆μ for nucleation and the initial saturation temperature T0.