On the entropy changes and fluctuations occurring near a tensile instability

Abstract

Several liquids exhibit an apparent loss of tensile strength (tensile instability) as their temperature is lowered. Assuming that such substances exhibit a true minimum in the PT projections of their spinodal curves, the thermodynamically consistent behavior that follows from this hypothesis displays a variety of unusual phenomena, of which the PVT aspects have been recently discussed. If, along the tensile instability isochore, the reciprocal compressibility vanishes linearly with respect to temperature (as is the case for a van der Waals fluid near the spinodal) an unusual metastable phase transition with discontinuous entropy and thermal expansion coefficient but continuous volume must occur if this isochore admits a metastable solution below the tensile instability temperature. The form of the specific heat divergence, as well as the equations of phase diagram loci of constant correlation length follow from the nature of the PVT surface in the vicinity of a tensile instability.