SUPERSATURATED ELECTROLYTE-SOLUTIONS - THEORY AND EXPERIMENT

Highly supersaturated electrolyte solutions can be prepared and studie d employing an electrodynamic levitator trap (ELT) technique. The ELT technique involves containerless suspension of a microdroplet thus eli minating dust, dirt, and container walls which normally cause heteroge neous nucleation. This allows very high supersaturations to be achieve d. A theoretical study of the experimental results obtained for the wa ter activity in microdroplets of various electrolyte solutions is base d on the development of the Cahn-Hilliard formalism for electrolyte so lutions. In the approach suggested the metastable state for electrolyt e solutions is described in terms of the conserved order parameter ome ga(r,t) associated with fluctuations of the mean solute concentration no. Parameters of the corresponding Ginzburg-Landau free energy functi onal which defines the dynamics of metastable state relaxation are det ermined and expressed through the experimentally measured quantities. A correspondence of 96-99% between theory and experiment for all solut ions studied was achieved and allowed the determination of an analytic al expression for the spinodal concentration n(spin) and its calculati on for various electrolyte solutions at 298 K. The assumption that sub critical solute clusters consist of the electrically neutral Bjerrum p airs has allowed both analytical and numerical investigation of the nu mber-size N-c of nucleation monomers (aggregates of the Bjerrum pairs) which are elementary units of the solute critical clusters. This has also allowed estimations for the surface tension alpha, and equilibriu m bulk energy beta per solute molecule in the nucleation monomers. The dependence of these properties on the temperature T and on the solute concentration n(o) through the entire metastable zone (from saturatio n concentration n(sat) to spinodal n(spin)) is examined. It has been d emonstrated that there are the following asymptotics: N-c=1 at spinoda l concentration and N-c = infinity at saturation.