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We report a thermodynamic study of the formation of tetrahydrofuran clathrate hydrate by explosive crystallization of water-deficient, near stoichiometric, and water-rich solutions, as well as of the heat capacity, C(p), of (i) supercooled tetrahydrofuran-H2O solutions and of the clathrate hydrate, (ii) tetrathydrofuran (THF) liquid, and (iii) supercooled water and the ice formed on its explosive crystallization. In explosive freezing of supercooled solutions at a temperature below 257 K, THF clathrate hydrate formed first. The nucleation temperature depends on the cooling rate, and excess water freezes on further cooling. The clathrate hydrate melts reversibly at 277 K and C(p) increases by 770 J/mol K on melting. The enthalpy of melting is 99.5 kJ/mol and entropy is 358 J/mol K. Molar C(p) of the empty host lattice is less than that of the ice, which is inconsistent with the known lower phonon frequency of H2O in the clathrate lattice. Analysis shows that C(p) of THF and ice are not additive in the clathrate. C(p) of the supercooled THF-H2O solutions is the same as that of water at 247 K, but less at lower temperatures and more at higher temperatures. The difference tends to become constant at 283 K. The results are discussed in terms of the hydrogen-bonding changes between THF and H2O.

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The real and imaginary components, Cp′ and Cp″, respectively, of the complex heat capacity, Cp*=Cp′−iCp″, of a molecular liquid have been measured in the temperature range of its vitrification and in the glassy state, and the effect of spontaneous structural relaxation has been determined in real time. Cp′ of the glassy state is found to decrease with time. Analysis shows that this is mainly due to the decrease of configurational entropy as the characteristic time of the Cp′ spectra increases and consequently the contribution from the unfrozen, faster modes of the α-relaxation process decreases. There may also be a significant decrease in the vibrational and anharmonic force contributions as the glass densifies. Interpretations in terms of the potential energy landscape model suggest that for each state of lower energy attained with time, the number of minima in the potential energy surface decreases, and the minima become deeper.

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Manuscript correlates microstructure and transport properties modification, which might suggest a way to prepare better performing SOFC electrolyte materials.