Liquid nucleation around charged particles in the vapor phase

Nucleation by a charged particle in fluids containing salt

We present a model to describe ion-induced nucleation in fluids. Nucleation is induced by a charged molecular aggregate, a large ion, a charged colloid, or an aerosol particle. This model generalizes the Thomson model to polar environments. Solving the Poisson-Boltzmann equation, we find the potential profiles around the charged core and calculate the energy. Our results are analytical in the Debye-Hückel limit and numerical otherwise. From the Gibbs free energy curve vs. nucleus size, we find the metastable and stable states and the energy barrier between them, for varying saturation values, core's charge, and amount of salt. The nucleation barrier decreases with increasing core charge or Debye length. We calculate the phase lines in the phase diagram of supersaturation and core charge. We find regions of one phase, electro-prewetting, spontaneous nucleation, ion-induced nucleation, and classical-like nucleation.

Phase lines in mean-field models with nonuniform external forces

We look at the influence of external fields on systems described by generic free energy functional of the order parameter. The external force may have arbitrary spatial dependence, and the order parameter coupling may be nonlinear. The treatment generalizes seemingly disparate works, such as pure fluids, liquid and polymer mixtures, lipid monolayers, and colloidal suspensions in electric fields, fluids, and nematics in gravity, solutions in an ultracentrifuge, and liquid mixtures in laser radiation. The phase lines and thermodynamic behavior are calculated at the mean-field level. We find a "surface" critical point that can be shifted to higher or lower temperatures than the bulk critical point. Below this point, the transition from a "gas" phase to a "liquid" phase is first-order, while above it, the transition is second-order. The second-order line is affected by the spatial dependence of the force, while the first-order line is universal. Moreover, the susceptibility may diverge at a finite location r. Several analytical expressions are given in the limit where a Landau expansion of the free energy is valid.

Electroprewetting near a flat charged surface

We look at the wetting of a pure fluid in contact with a charged flat surface. In the bulk, the fluid is a classical van der Waals fluid containing dissociated ions. The presence of wall and ions leads to strong dielectrophoretic and electrophoretic forces that increase the fluid's density at the wall. We calculate the fluid's profiles analytically and numerically and obtain the energy integrals. The critical surface potential for prewetting is obtained. In the phase diagrams, the line of first-order transition meets a second-order transition line at a critical point whose temperature can be higher or lower than the bulk critical temperature. The results are relevant to droplet nucleation around charged particles in the atmosphere and could possibly explain deviations from expected nucleation rates.