Empirical and theoretical models of equilibrium and non-equilibrium transition temperatures of supplemented phase diagrams in aqueous systems (IUPAC Technical Report)

Abstract

This paper describes the main thermodynamic concepts related to the construction of supplemented phase (or state) diagrams (SPDs) for aqueous solutions containing vitrifying agents used in the cryo-and dehydro-preservation of natural (foods, seeds, etc.) and synthetic (pharmaceuticals) products. It also reviews the empirical and theoretical equations employed to predict equilibrium transitions (ice freezing, solute solubility) and non-equilibrium transitions (glass transition and the extrapolated freezing curve). The comparison with experimental results is restricted to carbohydrate aqueous solutions, because these are the most widely used cryoprotectant agents. The paper identifies the best standard procedure to determine the glass transition curve over the entire water-content scale, and how to determine the temperature and concentration of the maximally freeze-concentrated solution.

Experimental evidence for excess entropy discontinuities in glass-forming solutions

“…82). When ice freezing takes place before glass formation, the remaining liquid part of the sample gets more concentrated with respect to the solute.…”

“…These discrepancies are explained in terms of a "fragile-to-strong" liquid transition of very dilute solutions which is experimentally inaccessible due to homogeneous ice freezing. 82,95 This transition and hence the c l 1 − c g 1 which should be used in Eq. (6) depend on the solute.…”

“…(6) depend on the solute. Corti et al 82 recommend 35 J K −1 mol −1 for fragile molecular solutions and a lower value for salt containing solutions.…”

Response to “Comment on ‘Experimental evidence for excess entropy discontinuities in glass-forming solutions”’ [J. Chem. Phys. 139, 047101 (2013)]

“…Therefore, c l 1 − c g 1 needs to be evaluated for each solute individually, as shown by LZ-ZKP. We believe that the description provided by LZZKP and the references cited therein 15,17 fully justify the procedure. Second, as a consequence of Eq.…”

“…9 However, there are different interpretations of such discontinuities upon heating. [11][12][13][14][15] It is possible that T g1 is the actual T g , and T g2 corresponds to the onset point of melting, usually referred to as T m . 14, 15 We do agree with BoLo that there is uncertainty concerning this attribution.…”