Masaharu Oguni

Heat capacity and glass transition of pure and doped cubic ices

Abstract Heat capacities of pure and KOH (mole fraction 1.8 × 10 −3 )-doped cubic ices were measured at nearly atmospheric pressures in the temperature ranges of 12–160 K and of 80–160 K, respectively. They were prepared from water at 250 MPa through the high pressure ice III and IX. The preparation and the subsequent heat capacity measurement were performed within a cell of an adiabatic high pressure calorimeter. A new glass transition, where the heat capacity showed a jump of 0.1 J K −1 mol −1 , was found at 140 K in the pure ice. The KOH doping caused a decrease in the glass transition temperature by about 30 K. For the bulk samples which had little surface, the enthalpy change during the irreversible cubic-hexagonal transformation at about 200 K was determined to be −(37.0 ± 0.8) J mol −1 . With the heat capacity data of the cubic and hexagonal ices, this value was converted to the enthalpy difference at OK, −(35.6 ± 0.8) J mol −1 .

Construction of an adiabatic calorimeter for a vapor-deposited sample and thermal characterization of amorphous butyronitrile☆☆☆

Abstract An adiabatic calorimeter for a vapor-deposited sample was newly constructed, and thermal properties of amorphous butyronitrile were studied in detail. The cryostat was cooled down to 10 K with a built-in refrigerator. The sample vapor was introduced through a filling tube into a calorimeter cell. During the deposition, the temperature of the cell was kept as low as possible by making mechanical-thermal contact with a refrigerant tank, while that of the tube was kept higher than the dew point of the vapor. A special device was made in order to minimize the heat flow from the tube to the cell. Butyronitrile vapor was deposited at 67 and 40 K in the first and the second experiments, respectively. Another kind of vitreous sample was prepared by rapidly cooling the liquid in comparison with the vapor-deposited vitreous samples. Heat capacities of the samples were measured in the temperature range from 15 to 175 K with an imprecision of about ±0.5%. Both the vapor-deposited and the liquid-quenched samples exhibited heat capacity jump characteristics of the glass transition of the same temperature, viz. 97 K. A large heat evolution amounting to 1.3 kJ mol −1 in total was observed in the case of vapor-deposited solid over a wide range of temperatures between the deposition temperature and the glass transition temperature. The microscopic picture for this heat evolution is discussed on the basis of the concept of the cluster structure for a liquid.

Enthalpy relaxation in vapor-deposited butyronitrile

Abstract Spontaneous enthalpy-evolution processes reported previously for vapor-deposited noncrystalline samples of solid butyronitrile were analyzed in terms of the equations of Kohlrausch, Williams and Watts (KWW), and of Adam and Gibbs (AG). The application of the KWW equation showed that the enthalpy relaxation deviated significantly from exponential behavior. The fractional exponent β characterizing the non-exponential nature was found to be 0.07 at 83.8 K, 0.11 at 89.7 K and 0.21 at 95.0 K. The significant deviation of β from unity reflects the extremely high fictive temperature of the specimen. The AG equation fitted the relaxation data well suggesting that the chemical potential Δμ hindering the cooperative rearrangement of molecules at each temperature was almost constant. The results were compared with other data derived from glasses prepared by conventional cooling of liquids.

Calorimetric study of pure and KOH-doped tetrahydrofuran clathrate hydrate†

Abstract The heat capacity of pure tetrahydrofuran (THF) clathrate hydrate was measured by an adiabatic calorimeter in the temperature range of 12–300 K. A glass transition having a heat capacity jump of 1.1 J K −1 (H 2 O-mol) −1 was newly observed at 85 K. Combined with previous dielectric data, this was shown to be related to proton configurational motion in the host hydrogen-bonded lattice. The experimental heat capacity of KOH-doped THF-hydrate reported in the previous paper was converted to the molar one of the hydrate by measuring its eutectic melting and making appropriate correction for unreacted ice and THF. Comparison of the heat capacities and entropies of the pure and KOH-doped samples gave new information on the mechanism of the transition observed in the KOH-doped sample.

Calorimetric study of thiophene from 13 to 300 K. Emergence of two glassy crystalline states

Abstract Heat capacities of stable and metastable phases of thiophene crystal were measured in the 13 to 300 K temperature range with an on-line automated adiabatic calorimeter. The enthalpies and entropies of the transitions and fusion that occurred at the following temperatures were measured: The condition of existence and the precise temperature of the II 2 -to-II 1 phase transition were found. A glass-transitional behaviour was observed around 42 K for the stable V phase and around 37 K for the metastable II 2 phase. Thermodynamic properties in the crystal and liquid states were calculated from our calorimetric results. Comparison of the calorimetric entropy with the spectroscopic value shows that the stable V phase has a residual entropy of (1.25 ± 0.9) J·K −1 ·mol −1 and the metastable II 2 phase one of (1.48 ± 0.9) J·K −1 ·mol −1 . Thus, both stable and metastable phases of thiophene crystal provide new examples of glassy crystals.

Thermo-analytical study of vapor-deposited n-alkanes†

Abstract Thermal properties of vapor-deposited n -butane, n -pentane, n -hexane and a binary system of n -butane and 1-butene were investigated by differential thermal analysis (DTA). Glass transitions were not observed below the crystallization temperature T cryst for the n -alkanes measured. It was evident from the results of the binary system that the crystallization in n -butane took place below the expected glass transition temperature T g . The ratio T b T fus was shown to be one good measure of the observability of the glass transition in the heating process of vapor-deposited samples as well as in the cooling of the liquid in the case of aliphatic hydrocarbons. The difference in crystallization tendency between n -alkanes and l-alkenes was discussed from the viewpoint of the molecular structure. It was shown that the empirical relation T g T fus ≅ 2 3 held for l-alkenes, but not for propane whose value was 0.53. Previous results of a radiothermoluminescence (RTL) study on similar vapor-deposited hydrocarbons were compared with the present results to elucidate the origin of RTL peaks.

Heat capacity and phase transition of tetrahydrofuran clathrate hydrate

Abstract Heat capacity of tetrahydrofuran clathrate hydrate THF·16.81H2O doped with KOH (x = 1.8 × 10−4 in the mole fraction of KOH in KOH and water) was measured in the temperature range 13–280 K. A sharp first-order phase transition having a large tail on the high temperature side was observed at 62 K and excess entropy due to the transition was determined to be 2.56JK−1 (H2O-mol)−1. From a comparison with thermal behavior of hexagonal ice, it was indicated that this transition was related to ordering of protons in the host lattice.

High‐pressure calorimetric study on the ice XI–Ih transition

A newly developed high‐pressure calorimeter was used to measure the XI–Ih phase transition of ice doped with KOH (mole fraction 1.3×10−3) at two pressures: 0 and 158.9 MPa. The transition temperature was found to be (71.6±0.1) and (74.0±0.1) K at the respective pressures, resulting in its mean pressure dependence of (0.015±0.001) K MPa−1. With this dependence and the theoretical entropy of the transition for the complete transformation of the XI phase, 3.4 J K−1 mol−1, the application of the Clausius–Clapeyron’s equation yields (0.051±0.003) cm3 mol−1 for the volume change associated with the transition. From these results in conjunction with other data, negative volume expansivity, as observed in the proton disordered phase Ih at low temperatures, was also suggested for the proton ordered phase XI.

Thermodynamic characterization of vapor-deposited amorphous solid☆

Abstract An adiabatic calorimeter designed for vapor-deposited sample has been applied to two molecular liquids, butyronitrile and 1-pentene, in order to characterize amorphous solid produced by vapor condensation. Comparisons are made between thermodynamic behavior of the vapor-deposited (VQ) and liquid-cooled (LQ) amorphous solids of both samples. It can be concluded that both the LQ and VQ solids exhibit essentially the same phenomena; the glass transition, residual entropy, and enthalpy relaxation. These are the reflection of the metastability and the non-equilibrium nature of both amorphous solids. From a quantitative viewpoint, however, the two types of amorphous solid behave differently. The VQ samples show the enthalpy relaxation occurring just above the temperature of deposition, and have larger residual entropy compared to the LQ samples. These results indicate the effective extraction of the kinetic energy of molecules during the process of condensation from vapor to amorphous solid.

Calorimetric and dilatometric studies on the phase transitions of crystalline CH3NH3I

Calorimetric and dilatometric studies on CH3NH3I(cr) were carried out with two types of adiabatic calorimeter in the temperature ranges 14 to 300 K and 100 to 300 K, respectively. Two phase transitions were observed, one at 220 K (room-temperature α′ to stable β′) and the other at 166.1 K (undercooled α′ to metastable δ). Comparison of the entropies of the β′ and δ phases indicated that both phases are ordered at T → 0. The molar entropy change ΔtrsSm and molar volume change ΔtrsVm associated with the β′-to-α′ transition were found to be 13.5 J · K−1 · mol−1 and 2.98 cm3 · mol−1, respectively. The superheating phenomenon of the transition was shown to depend strongly on pressure. This was concluded by comparing dTtrsdp calculated from ΔtrsSm and ΔtrsVm with that observed by high-pressure d.t.a. In relation to the δ-to-α′ transition, the states of overall rotational motion of the CH3NH3+ ion in the α′ phase are discussed on the basis of the interrelation between the orientational degeneracy and the magnitude of the entropy due to the mode.