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.

Two-structure thermodynamics for the TIP4P/2005 model of water covering supercooled and deeply stretched regions

“…This was a serious limitation in the applications of two-structure thermodynamics, especially in view of the fact that the shape of the spinodal and its possible connection to supercooled water's anomalies has been debated since the 1980s. 1,[32][33][34][35][36][37][38][39][40][41] In 1982 Speedy 32 proposed an interpretation of the thermodynamic anomalies of metastable water. He conjectured that " a continuous line of stability limits bounds the superheated, stretched, and supercooled states," which would cause the increase in response functions upon supercooling.…”

Cooperative molecular motions in water: The liquid-liquid critical point hypothesis

“…For example, the collective excitations that occur at low frequency and large wave vector [71] have been the object of much recent work [72,73]. Also, the full implications of a re-entrant spinodal possibility [74][75][76][77] may not have been fully incorporated into our understanding of water. The minimum exhibited by the adiabatic compressibility in atmospheric pressure experiments [78] is of potential relevance since a maximum in any quantity that would be singular at a spinodal may be relevant to placing the critical point at a larger pressure than atmospheric.…”

Two-dimensional lattice-fluid model with waterlike anomalies

“…After this point the line becomes negatively sloped and joins continuously the stability limit with respect to the ordered ice phase. The TMD locus intersects the limit of stability in its minimum in the T-P plane, according to the predictions of Speedy and Debenedetti [37][38][39][40][41][42][43], based on thermodynamic consistency arguments. In fact, the TMD locus causes the liquid limit of stability line to retrace, giving rise to a tensile strength maximum and to a continuous boundary.…”