Curvature effect on the physical boundary of metastable states in liquids

The physical boundary of metastable states, the kinetic spinodal, is introduced as a locus where the lifetime of metastable state becomes shorter than a relaxation time to local equilibrium. The theory does not contain any adjustable parameters. If the surface tension is known, the kinetic spinodal is completely determined by the equation of state only. The curvature effect on the surface tension and nucleation barrier is considered and a general, curvature-corrected, equation for the kinetic spinodal is developed. The theory was tested against experimental data for the homogeneous nucleation limit of superheated, stretched, and supercooled water. In all cases, good agreement between theoretical predictions and experimental data was achieved. We find that in water, the Tolman length is negative and the curvature effect increases the surface tension and the nucleation barrier. The glass transition in supercooled water is also discussed. The high-temperature limit for glassy states is introduced as a second root of the kinetic equation in supercooled fluids.