(335ab) Metastable Cluster Intermediates In The Condensation Of Charged Macromolecule Solutions

We examine the possibility of a two-step nucleation to the bulk condensation transition that proceeds via a metastable liquid cluster intermediate having some preferred size. The metastable intermediate is stabilized by electrostatic repulsion, which becomes screened by small mobile ions at sufficiently large cluster sizes, thus allowing the eventual condensation to a bulk phase. Our calculation employs a capillary model for the cluster and the electrostatic interactions are treated using the Poisson-Boltzmann approach. The metastable liquid cluster is predicted to exist for a range of parameters that are well within the confines of physical parameters encountered in solutions of charged particles (e.g. proteins, colloidal particles, and polyelectrolytes). In addition, for an even broader parameter space, our model corroborates the well-studied formation of preferred-size clusters when no bulk, condensed phase exists.