Osamu Yamamuro

Heat capacities and glass transitions of 1-propanol and 3-methylpentane under pressure. New evidence for the entropy theory

The heat capacities of 1-propanol and 3-methylpentane were measured in the temperature range 50–180 K (50–130 K for the latter) and at three different pressures (0, 108, 198 MPa) using an adiabatic high-pressure calorimeter. For both substances, the glassy state was readily realized by cooling the liquid and glass transitions were observed calorimetrically at every pressure. Thermodynamic quantities associated with the fusion of the crystalline phase were measured at three pressures for 1-propanol and at 108 MPa for 3-methlpentane. Pressure dependences of the glass transition and fusion were accurately determined. Experimental data for the entropy of fusion and the heat capacity difference between the glass and the liquid were combined to calculate the temperature dependence of the configurational entropy, Sc, at each pressure. The pressure dependence of the Kauzmann temperature, T0, at which Sc tends to vanish, was also determined. It was found that the quantity TSc was almost constant at Tg for respective pressures, indicating the validity of the entropy theory proposed by Adam and Gibbs.

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 .

Heterogeneous Slow Dynamics of Imidazolium-Based Ionic Liquids Studied by Neutron Spin Echo

We have investigated structure and relaxation phenomena for ionic liquids 1-octyl-3-methylimidazolium hexafluorophosphate (C8mimPF6) and bis(trifluoromethylsulfonyl)imide (C8mimTFSI) by means of neutron diffraction and neutron spin echo (NSE) techniques. The diffraction patterns show two distinct peaks appeared at scattering vectors Q of 0.3 and 1.0 Å(-1). The former originates from the nanoscale structure characteristic to ionic liquids and the latter due to the interionic correlations. Interestingly, the intensity of the low-Q peak drastically grows upon cooling and keeps growing even below the glass transition temperature. The NSE measurements have been performed at these two Q positions, to explore the time evolution of each correlation. The relaxation related to the ionic correlation (ionic diffusion) is of Arrhenius-type and exhibits nonexponential behavior. The activation energy (Ea) of the ionic diffusion, which is linked to viscosity, depends on the type of anion; the larger is the anion size, the smaller Ea becomes for most of anions. On the other hand, two kinds of relaxation processes, slower and faster ones, are found at the low-Q peak position. The most significant finding is that the fraction of the slower relaxation increases and that of the faster one decreases upon cooling. Combining the NSE data with the diffraction data, we conclude that there exist two parts in ILs: one with the ordered nanostructure exhibiting the slow relaxation, and the other with disordered structure showing faster relaxation. The structure and dynamics of ILs are heterogeneous in nature, and the fraction of each part changes with temperature.

p-T phase relations of CH3NH3PbX3 (X = Cl, Br, I) crystals

Abstract Pressure-temperature phase relations of CH 3 NH 3 PbX 3 (X = Cl, Br, I) crystals were studied by using a high pressure DTA apparatus in the range between 0.1 Pa and 200 MPa. A triple point was found in each compound below 100 MPa. By pressurization, the low pressure phases disappeared at the triple point in the chloride and bromide while a new high-pressure phase appeared in the iodide. The pressures and temperatures of the triple points are 75.1 MPa, 175.7 K for CH 3 NH 3 PbCl 3 , 43.2 MPa, 152.9 K for CH 3 NH 3 PbBr 3 , and 84.8 MPa, 176.2 K for CH 3 NH 3 PbI 3 . All the boundaries between the cubic and tetragonal phases are upward convex and that of the iodide has a maximum at about 120 MPa. Other phase boundaries are essentially straight lines in the measured pressure and temperature ranges. By the use of the Clausius-Clapeyron equation, the transition volumes were calculated from the slopes of the phase boundaries and the transition entropies obtained in a previously published calorimetric experiment ( J. Phys. Chem. Solids 51 , 1383 (1990)).

Hierarchical structure and dynamics of an ionic liquid 1-octyl-3-methylimidazolium chloride

We have performed the heat capacity, neutron diffraction, and neutron quasielastic scattering measurements of an ionic liquid 1-octyl-3-methylimidazolium chloride (C8mimCl). The heat capacity data revealed that C8mimCl exhibits a glass transition with a large heat capacity jump at T(g) = 214 K, which is lower than T(g) of C4mimCl with a shorter alkyl-chain. In the neutron diffraction measurement for a deuterated analogue, d-C8mimCl, the peaks associated with the inter-domain, inter-ionic, and inter-alkyl-chain correlations appeared at (3, 11, and 14) nm(-1), respectively. The temperature dependence of these peaks indicates that the packing of the alkyl-chains becomes more compact and the domains become more vivid and larger as decreasing temperature. The quasielastic neutron scattering measurements using neutron spin echo and time-of-flight type instruments demonstrated that C8mimCl has faster relaxations probably owing to the alkyl-group and a slower relaxation owing to the ions. The latter relaxation, which is related to the glass transition, is of non-exponential as in the α relaxation of glass-forming molecular liquids. The relaxation of domains could not be observed in the present experiment but should have relaxation times longer than 100 ns. This is the first report to clarify temperature dependence of the hierarchical structure and relaxations simultaneously for a typical ionic liquid.

Thermodynamic fragility and kinetic fragility in supercooling liquids: A missing link in molecular liquids

Ito, Moynihan, and Angell [Nature 398, 492 (1999)] compared the kinetic and thermodynamic measures of a glassformer’s “fragility.” For the liquids they considered which include molecular, covalent, and ionic substances, thermodynamic fragility and kinetic fragility follow the same order, suggesting that the thermodynamic data alone may be sufficient to determine the kinetic fragility of a liquid. Here we restrict the comparison to a large number of molecular glass-forming liquids, and find breakdowns of the proposed correlation. The absence of an immediate connection between thermodynamic and kinetic fragilities at least in molecular liquids may be due to the effect of kinetic factors and cooperative many-body molecular dynamics. The development of a relation between them requires taking into consideration the cooperative many-body molecular dynamics. The latter governs, in conjunction with thermodynamics, the kinetics of glass-forming liquids, and thus is the missing link between the two.

Isotopic Polymorphism in Pyridine

The ab initio calculation of the relative stabilities of isomers of gas phase molecules rates as one of the outstanding scientific achievements of the twentieth century. Our understanding of the structure of solid state is, by comparison, much less well advanced. The problem is illustrated by the crystal structure of pyridine. Pyridine (C5H5N or ‘h5’ hereafter) is one of the simplest heteroaromatic compounds but its crystal structure (phase h5-I) is unusually complicated, having four independent molecules in the asymmetric unit (Z’ = 4). [1] Price et al. have surveyed the potential for polymorphism in pyridine using ab initio crystal structure prediction methods, finding over a dozen crystal structures that were energetically competitive with h5-I. [2] In parallel with Price’s theoretical work an intense experimental search was made by one of us (RB group) for new low-temperature polymorphs of pyridine. Though all attempts to crystallize h5 failed to yield anything but the h5-I phase, crystallization of pyridine-d5 (d5) from pentane yielded a new phase, d5-II, at 188 K. Recrystallization from a low-melting solvent such as pentane has been shown in the past to circumvent hightemperature phases because saturation of the solution occurs below the temperature of the phase transition. [3] The new d5-II phase has one molecule in the asymmetric unit (Z’ = 1), but does not correspond to any of the predicted polymorphs of h5. The effect of temperature on the crystal structure of pyridine-d5 was subsequently investigated further using neutron powder diffraction. The sample was ground at 77 K [4] and then rapidly cooled to 2 K. The powder pattern was successfully modelled as d5-I (see Fig. S1a in the Supplementary Information). The sample was then warmed in steps of 2 K, with patterns being acquired at each temperature. When the sample reached 170 K it began to undergo a sluggish phase transition into d5-II. After collecting a clean d5-II neutron powder

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.

Linear trinuclear Zn(II)-Ce(III)-Zn(II) complex which behaves as a single-molecule magnet.

Linear Zn(II)-Ce(III)-Zn(II) complex, which involves only one 4f electron as a spin source, behaves as an SMM. Easy-axis magnetic anisotropy for the ground (2)F(5/2) state of Ce(III) was achieved by a uni-axial crystal field, which is formed with four phenoxo oxygens as axial donors with the other five oxygens as equatorial donors.

Heat capacities and glass transitions of ground amorphous solid and liquid-quenched glass of tri-O-methyl-ß-cyclodextrin

Abstract Amorphous solid of tri-O-methyl-s-cyclodextrin (TMCD) was formed by grinding crystalline samples with a vibrating mill at room temperature. Heat capacities of the ground amorphous solid (GAS), liquid-quenched glass (LQG) and crystal of TMCD were measured with an adiabatic calorimeter in the temperature range 13–375 K. The heat capacity of the GAS was the same as the LQG in the whole temperature range. The glass transition was observed at 345 K for both amorphous solids. The heat capacities of the crystal were ∼3% lower than those of the amorphous solids. During the heat capacity measurement of the LQG, a typical exothermic effect due to the enthalpy relaxation was observed in the temperature range 315–345 K. On the other hand, much larger enthalpy relaxation having unusual temperature dependence occurred for the GAS in the same temperature range. The released configurational enthalpy of the GAS was more than twice that of the LQG.