(754a) Nucleation in the Highly Supersaturated Boundary Layer During Solvent Freeze-Out

Nucleation kinetics, induction times, and metastable zone widths are often modeled in quiescent, quasi-steady, and/or spatially uniform concentration fields.  However, freezing an aqueous solvent can concentrate the solute and effectively increase the supersaturation.  During the freezing process, a boundary layer of giant supersaturation develops ahead of the moving ice front.  We solve for the time-dependent concentration in the boundary layer under conditions where the growing ice perfectly excludes the solute.  We then develop stochastic models of nucleation in the boundary layer.  Whether heterogeneous on the ice surface, or homogeneous in the boundary layer, nucleation is dramatically accelerated by the growing ice.  For methane hydrates, which form at similar conditions to ice, induction times for nucleation can be reduced by as much as 10⁸⁰ times because of the moving supersaturation zone.