Shuichi Takahara

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.

Low temperature phase properties of water confined in mesoporous silica MCM-41: Thermodynamic and neutron scattering study

The phase properties of water confined in mesoporous silica MCM-41 were investigated over a temperature range of 100-298 K as a function of pore size by specific heat capacity and inelastic neutron scattering (INS) measurements. The water content of the samples was carefully controlled to ensure the capillary filled state and no overloading of water. The values of heat capacity of the pore water are higher than those of bulk ice and liquid water over the whole temperature range measured. The contribution of water in the inner part of pores (abbreviated as the internal water) was elucidated by using the heat capacity data of monolayer water measured. The entropy of the internal water was then estimated from integration of the heat capacity of the internal water. The entropy values of the internal water increase by confinement in the pores of MCM-41 in both liquid and frozen regions, indicating an increase in the deformation of the structure and∕or a change in the dynamics in both regions. The INS spectra show the density of states for the librational motion of water frozen at 50 K, suggesting that the confined water is similar to amorphous ice rather than to crystalline ice. When the sample is warmed to melt, the band edge of the librational motion for water frozen in large pores (diameter of 3.6 nm) shifts to a lower energy side, indicating the weakening of intermolecular hydrogen bonds. For water in small pores (2.1 nm), on the contrary, the librational band shifts slightly to a higher energy side, suggesting the low density liquid to high density liquid transition (L-L transition) at 225-250 K. A plausible mechanism of the L-L transition of water in confinement is proposed in terms of incomplete growth of homogeneous nucleation of ice due to an interfacial free energy effect to inhibit crystallization of water confined in small pores.

Structural relaxations of 3-methylpentane and 1-propanol under high-pressure: temperature- and pressure-jump methods

Abstract The structural relaxations of 3-methylpentane and 1-propanol have been investigated around their glass transition temperatures at several constant pressures between 0 and 200 MPa. The structural relaxation was observed as a temperature evolution due to the enthalpy relaxation by using a high-pressure adiabatic calorimeter. The initial states for the relaxations (glassy states) were prepared through two different paths on the pressure-temperature plane; one was a rapid cooling at constant pressure (temperature jump: TJ) and the other a rapid pressurization at nearly constant temperature (pressure jump: PJ). It was found that both of the relaxation processes of the PJ and TJ glasses were quite non-exponential. The relaxation function of the PJ glass was different from that of the TJ glass. The relaxations for the TJ experiments were well analyzed in terms of the Adam-Gibbs (entropy) theory in the entire pressure and temperature regions investigated.

Development of an adiabatic calorimeter for simultaneous measurement of enthalpy and volume under high pressure

A novel adiabatic calorimeter was constructed for simultaneous measurement of enthalpy and volume under high pressure. The calorimeter works under constant pressure up to 100 MPa and in the temperature range 80–380 K. The sample is pressurized hydrostatically by using a liquid pressure transmitting medium. The sample volume is measured with a new type of dilatometer using bellows installed in the cell. The dilatometer has two resolution modes (high and low) with different scanning range. As the calibration and test experiments, the heat capacities and volumes of toluene and water were measured at 0.1 and 50.1 MPa in the temperature range between 275 and 380 K. In the low resolution mode, the accuracies of heat capacity and volume were ±0.2% and 20 ppm of total, respectively. The test of the volume measurement in the high resolution mode showed that the resolution was ±0.1 ppm of total sample volume, which is ∼ ten times better than that of the previous best dilatometer. To demonstrate the performance of t...

Dielectric study of crystalline thiophene

Abstract Complex dielectric permitivity of thiophene was measured in the temperature range 20–290 K and in the frequency range 100 Hz–1 MHz. Sharp peaks in the real and imaginary parts of dielectric permittivity resembling ferroelectric transition were found at the V–IV transition in the stable-phase sequence. The dielectric anomaly was characterized by a large thermal hysteresis and a strongly frequency-dependent permittivity. Dielectric dispersions due to the orientational motion of thiophene molecules were observed in both stable and metastable sequences. The relaxation times and the activation enthalpies calculated from the dispersion data were consistent with previous results obtained by calorimetry.

Heat capacities of glass-forming molecular liquids: negative evidence for the liquid-liquid transition

The heat capacity of the supercooled liquid phase of 3-methylpentane has been measured with a high-precision adiabatic calorimeter. Negative evidence was obtained for the occurrence of a liquid-liquid transition currently discussed in relation to the mode-coupling theory of liquid states. A search for similar transitions in 1-butene and 1-pentene also gave negative results.

High physisorption affinity of water molecules to the hydroxylated aluminum oxide (001) surface.

The adsorption mechanism of water on the hydroxylated (001) plane of α-Al(2)O(3) was studied by measuring adsorption isotherms and GCMC simulations. The experimental adsorption isotherms for three α-Al(2)O(3) samples from different sources are typical type II, in which adsorption starts sharply at low pressures, suggesting a high affinity of water to the Al(2)O(3) surface. Water molecules are adsorbed in two registered forms (bilayer structure). In the first form, water is registered at the center of three surface hydroxyl groups by directing a proton of the water. In the second form, a water molecule is adsorbed by bridging two of the first-layer water molecules through hydrogen bonding, by which a hexagonal ring network is constructed over the hydroxylated surface. The network domains are spread over the surface, and their size decreases as the temperature increases. The simulated adsorption isotherms present a characteristic two-dimensional (2D) phase diagram including a 2D critical point at 365K, which is higher than that on the hydroxylated Cr(2)O(3) surface (319 K). This fact substantiates the high affinity of water molecules to the α-Al(2)O(3) surfaces, which enhances the adsorbability originating from higher heat of adsorption. The higher affinity of water molecules to the α-Al(2)O(3) (001) plane is ascribed to the high compatibility of the crystal plane to form a hexagonal ring network of (001) plane of ice Ih.

Restricted Rotational Motion of InterlayerWaterMolecules in Vanadium Pentoxide Hydrate, V2O5·n D2O, as Studied by Deuterium NMR

The rotational behavior of the interlayer water molecules of deuterated vanadium pentoxide hydrate, V2O5.nD2O, was studied by solid-state deuterium NMR for the mono- and double-layer structures of the adsorbed water molecules. The rotational motion was anisotropic even at 355 K for both the mono- and double-layer structures. The 180° flipping motion about the C2-symmetry axis of the water molecule and the rotation around the figure axis, which makes an angle Ɵ with the C2-axis, occurred with the activation energy of (34±4) and (49±6) kJmol-1, respectively. The activation energies were almost independent of the mono- and double-layer structures of the water molecules, but the angle Ɵ made by the two axes varied from 33° for the monolayer to 25° for the double-layer at 230 K. The angle started to decrease above 250 K (e. g. the angle was 17 at 355 K for the double-layer structure). The results indicate that the average orientation of the water molecules in the two dimensional interlayer space depends on the layer structure and on the temperature. From the deuterium NMR spectrum at 130 K, the quadrupole coupling constant e2Qq/h = 240 kHz and the asymmetry parameter η= 0.12 were deduced. These values indicate the average hydrogen bond distance R(O H) = 2.0 Å for the D2O molecules in the 2D-interlayer space

Dielectric study on two dynamic phases of 1-propanol confined in mesopores of MCM-41

Two dynamic phases were recognized on the 1-propanol molecules confined in MCM-41 with pore diameters d = 2.1, 2.4, 2.7 and 3.6 nm by dielectric measurements, in which two types of confined states of liquid were investigated: surface-adsorbed (sa) and pore-filled (pf) liquid. The dielectric measurements in the frequency range 103–107 Hz and temperature range 120–300 K showed that the molecular motions became slower in the following order: bulk, pf and sa liquid, which is the same order as for methanol and ethanol confined in MCM-41 reported previously. For pf samples, two relaxation components, which correspond to molecules near the pore surface and at the center of the pores, were observed separately. This is somewhat different from the behavior of methanol and ethanol confined as pf state in which two relaxation components were also detected but a clear separation between them was not observed. This implies that 1-propanol molecules near the pore wall interact weakly with those at the central part of th...

Interaction of Ultrafine Titanium Oxide Particles with Layered Vanadium Oxide Hydrate

Vanadium pentoxide hydrate was pillared with ultrafine titanium dioxide particles to form expanded layered structure (∼20 A) and thereby forming microporous substance (diameter =∼10 A). Porous structure formation and adsorption of some toxic gases (CO and NO) were discussed.