The effect of ion solvation on ion-induced nucleation—A generalized Thomson model

We present a model for ion-induced nucleation, focusing on the effect of dissociated ions embedded in the fluid surrounding a charged core or colloid. The model includes the ions' direct electrostatic energy and preferential solvation. The integrated ions' free energy has two terms: The first can be short- or long-range, depending on their density. The second is proportional to the nucleus' volume and can shift the state from undersaturation to supersaturation at high ion concentration. The inclusion of the Gibbs transfer energies of ions in the free energy leads to a modified Poisson-Boltzmann equation for the potential around the core. The integrated ions' free energy is added to the fluids' interfacial and bulk terms to establish a generalized Thomson model. In the Debye–Hückel limit, the model is solved analytically, while in the nonlinear regime, it is solved numerically. The state diagram in the plane of saturation and core charge includes regions with a homogeneous phase, electro-prewetting, metastable vapor, metastable nucleus, and spontaneous nucleation states. The lines separating these regions depend sensitively on the preferential solvation. Our model shows nucleation asymmetry to the sign of the nucleus' charge. This sign asymmetry is due to the Gibbs transfer energies of ions.