Chemical oscillations and instabilities .100. Unstable supersaturated solutions of gases in liquids and nucleation theory

Limiting supersaturations for dissolved gases manifested by gas evolution oscillators and by direct experiments cannot be accounted for by the application of classical nucleation theory (CNT). The theory predicts bubbles containing 10(4)-10(5) molecules at nucleation, with Helmholtz energies of ca. 10(4)kT per bubble, much too high for homogeneous nucleation to occur spontaneously in a finite time. We investigate alternative unstable structures ('blobs') which do not have well-defined interfaces, which may exist transiently at the point of nucleation as the precursors of true bubbles and which circumvent the need for a large Helmholtz energy for their formation. Effects due to global or local depletion of the solution concentration at nucleation are also considered.