Enthalpic and entropic phase transitions in high energy density nuclear matter

Features of Gas-Liquid (GL) and Quark-Hadron (QH) phase transitions (PT) in dense nuclear matter are under discussion in comparison with their terrestrial counterparts, e.g. so-called "plasma" PT in shock-compressed hydrogen, nitrogen, xenon etc. Both, GLPT and QHPT, when being represented in widely accepted $T - μ$ diagram, are often considered as similar, i.e. amenable to one-to-one mapping by simple scaling. It is argued that this impression is illusive and that GLPT and QHPT belong to different classes: namely, GLPT is typical \emph{enthalpic} (VdW-like) PT while QHPT ("deconfinement-driven") is typical \emph{entropic} PT like hypothetical ionization- and dissociation-driven phase transitions in hot and dense hydrogen, nitrogen etc. of megabar pressure range. Newly introduced terms "enthalpic" and "entropic" PT, are defined and clarified in their illustrative comparison successively from $T - μ$ to $P - T$ and $P - V$ phase diagrams for GLPT and QHPT from one side (dense nuclear plasma) vs. GLPT and "plasma" (or "dissociative") PTs from another side (electromagnetic plasma). Fundamental difference in topology of binodal and spinodal curves for enthalpic and entropic phase transitions are discussed and illustrated. Multilayered structure of thermodynamic surfaces $T(P,V)$, $U(P,V)$, $S(P,V)$ etc. as basic origin for intrinsic anomalous properties of all entropic PTs, is stressed.

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