Non-equilibrium freezing behaviour of aqueous systems

Abstract

The tendencies to non-equilibrium freezing behaviour commonly noted in representative aqueous systems derive from bulk and surface properties according to the circumstances. Supercooling and supersaturation are limited by heterogeneous nucleation in the presence of solid impurities. Homogeneous nucleation has been observed in aqueous systems freed from interfering solids. Once initiated, crystal growth is often slowed and, very frequently, terminated with increasing viscosity. Nor does ice first formed always succeed in assuming its most stable crystalline form. Many of the more significant measurements on a given system can be combined and displayed in the form of a ‘supplemented phase diagram’, the latter permitting the simultaneous representation of thermodynamic and non-equilibrium properties. The diagram incorporates equilibrium melting points, heterogeneous nucleation temperatures, homogeneous nucleation temperatures, glass transition and devitrification temperatures, recrystallization temperatures, and, where appropriate, solute solubilities and eutectic temperatures. Taken together, the findings on model systems aid the identification of the kinetic and thermodynamic factors responsible for the freezing - thawing survival of living cells.