Kinetic boundary of metastable states in superheated and stretched liquids

A physical boundary of metastable states – kinetic spinodal is introduced as a locus where the mean time of formation of a critical nucleus becomes shorter than a characteristic time governing the decay of fluctuations to local equilibrium. To extend this definition at negative pressures a new thermodynamic relation for the nucleation barrier has been obtained. The kinetic spinodal in this approach is completely determined by the equation of state and by the surface tension of the liquids. Starting from the critical point the kinetic spinodal first traces the limit of stability of superheated liquid, then passes through the negative pressures, thus defining the limit of stability for stretched liquid. For a comparison of the results of calculations with the experimental data in the superheated and stretched fluids the thermodynamic properties of methane and water in the metastable region are considered.