Homogeneous nucleation and growth of ice from solutions. TTT curves, the nucleation rate, and the stable glass criterion

Using water-in-oil emulsion samples to avoid, for the most part, heterogeneous nucleation, the crystallization of ice from a series of aqueous LiCl solutions has been studied isothermally, using differential calorimetry to monitor the process through the release of the heat of crystallization. The classical form of the time-temperature transformation TTT curve has thereby been directly observed for the first time for cystallizing supercooled liquids, and its movement with concentration changes has been determined. The conditions of observation are such that each ∼3 μ diameter droplet is multiply nucleated during the time of observation. At temperatures well above the "nose" of the TTT curve, where multiple nucleation does not occur, a new phenomenon-in which the rate of crystallization increases with increasing temperature of observation-is encountered. It seems probable that this is due to some heterogeneous process perhaps involving a reaction at the water-oil-surfactant interface to account for the positive temperature coefficient. The results in the homogeneously nucleated region correlate well with the much longer time scale studies reported recently on the basis of time-dependent conductivity measurements. Using approximate diffusivity data for water in this system, the combined crystallization data can be analyzed to yield nucleation rates which are in reasonable agreement with the results of recent small angle neutron scattering studies on this system.