Kikujiro Ishii

Character of devitrification, viewed from enthalpic paths, of the vapor-deposited ethylbenzene glasses.

Enthalpic path and enthalpy-relaxation rates of ethylbenzene glasses prepared by vapor deposition at various temperatures, T(D), were examined on heating intermittently with a high-precision adiabatic calorimeter. It was confirmed that when T(D) is in the range 0.79-0.96T(g), the enthalpies elucidated at their preparation temperatures, i.e., T(D), are lower than those of the liquid-cooled glass. The fictive temperature T(f) at which the enthalpy path of each glass crosses the enthalpy curve expected for the equilibrium supercooled liquid was observed to be lowest when T(D) = 0.92T(g) = 105 K. The glasses revealed two remarkable characteristics: first, the temperature of the peak in the endothermic effect, which corresponds to the temperature T(g,dev) of the steepest devitrification, was observed to increase in correlation with the low-enthalpic nature of the glasses. Second, the devitrification manner was quite different between the glasses with T(D) < 0.92T(g) and T(D) ≥ 0.92T(g), even if the two glasses have the same T(f); the former devitrified gradually and the latter relatively sharply.

Raman spectral changes of neat CO2 across the ridge of density fluctuation in supercritical region

Density dependence of Raman spectra for carbon dioxide was studied along the isotherm in the temperature region 0.96⩽T/Tc⩽1.06 and the density region 0<ρ/ρc<2. Spectrum in the small-wavenumber region below 100 cm−1 and that in the region of the 2ν2 intramolecular band, i.e. one of the Fermi dyad, were carefully measured and analyzed. The results are interpreted by assuming the presence of the gas- and liquid-like regions in the supercritical region separated by the ridge of density fluctuation.

POLARIZED MEMORY EFFECT IN THE DEVICE INCLUDING THE ORGANIC CHARGE-TRANSFER COMPLEX, COPPER-TETRACYANOQUINODIMETHANE

The polarized memory effect, in which the switching between the on and off states depends on the polarity of the bias voltage, was found in the device including the film of the organic charge‐transfer complex, copper‐tetracyanoquinodimethane (Cu‐TCNQ). The device consists of three layers, Al/Cu‐TCNQ/Cu. The dc I‐V characteristics and the dielectric behavior up to 106 Hz were studied. The number of the charge carriers which make the dielectric response below 103 Hz increases in the on state. The mechanism of the switching is briefly discussed.

Local density enhancement in neat supercritical fluid due to attractive intermolecular interactions

Abstract Short-range structure in the neat supercritical fluid consisting of polar molecules is investigated by measuring Raman spectrum of fluoroform (CHF3) at reduced temperature Tr=T/Tc=1.02. The spectra are analyzed by the Schweizer–Chandler model, and the spectral shift is decomposed into attractive and repulsive components as a function of density varied by a factor of 50. The attractive component shows larger shift than the one anticipated from the uniform molecular distribution. A local density enhancement due to the attractive intermolecular interactions is definitely observed in the neat supercritical fluid and evaluated against bulk density.

Raman spectra and phase transition of the phenothiazine crystal

Abstract Polarized Raman spectra of single crystals of phenothiazine which undergoes a phase transition around 250 K and is ferroelastic in the low-temperature phase were measured in the lattice-vibrational region for temperatures ranging from 89 to 300 K. The spectra of the high- and low-temperature phases obey the selection rules required for the orthorhombic and monoclinic structures, respectively. Anomalous temperature dependences are observed in the frequency, intensity and linewidth of a band appearing in the lowest-frequency region. This band is attributed mainly to a librational motion of the molecule, and is important in the evaluation of this phase transition. A gradual change of the molecular orientation is inferred to occur over a wide temperature interval in the low-temperature phase along the vibrational coordinate of the above libration. Another strong, low-frequency band, which is characteristic of the phenothiazine spectra, is suggested to arise from mixing between intramolecular and lattice vibrations. This mode is considered to play some role in the phase transition too. The interaction between the low-frequency optical modes and the acoustic modes is briefly discussed in connection with the ferroelasticity of the low-temperature phase. The transition temperature depends on the quality of the specimen; the correct transition temperature is found to be 248.8 K and slightly lower than the previously reported value.

Nonequilibrium and relaxation in deeply supercooled liquid of isopropylbenzene obtained through glass transition from vapor-deposited glass.

Change in the light interference in film samples of isopropylbenzene was studied in the supercooled liquid (SCL) state. Samples were originally formed as glass by vapor deposition on a cold substrate and the intensity of laser light reflection from them was monitored as the temperature was raised with a constant rate up to the region of the SCL state above the glass-transition temperature. Two types of periodic changes in the light intensity were observed in the SCL state. One was attributed to the interference condition change accompanying the structural relaxation from the low-density SCL to the equilibrium SCL state, and the other was due to the gradual expansion of the high-density SCL. Analysis of the latter change revealed that the initial density of the high-density glass was larger than that estimated in our previous paper.

Molar Volumes of Ethylcyclohexane and Butyronitrile Glasses Resulting from Vapor Deposition: Dependence on Deposition Temperature and Comparison to Alkylbenzenes

Molar volumes (Vm) of vapor-deposited ethylcyclohexane (ECH) and butyronitrile (BN, sometimes called butanenitrile) glasses were studied as a function of deposition temperature (Td). ECH glasses deposited at Td sufficiently below their glass-transition temperature (Tg) exhibited changes in Vm on heating similarly to alkylbenzenes. At Td close to Tg, ECH formed dense glasses as alkylbenzenes do, although these glasses were only slightly more dense than its supercooled liquid (SCL) states at the same temperatures. For BN, no indication of the formation of dense glasses was observed even at Td close to Tg, and the variations in Vm with the temperature elevation were different from those of alkylbenzenes. Analysis of the initial Vm of the deposited glasses of different compounds demonstrated that its Td-dependence was well correlated with the steepness index (m) of the corresponding SCL. Quantum-chemical calculations concerning dimer formation by the studied compounds showed that the hydrogen bond between a C-H bond in the alkyl group and π-electrons in the phenyl ring stabilizes the alkylbenzene dimers, suggesting the possibility of the dense glass formation and large m of these compounds. The small m value of BN was also discussed on the basis of the calculation results.

Relaxational Molecular Motions in Simple Organic Liquids: Studies with Low‐Wavenumber Depolarized Raman Spectroscopy

Depolarized Raman spectra of simple organic liquids in the wavenumber region 0–200 cm-1 were measured. The data were analyzed by assuming model spectral functions in this entire wavenumber region but by putting stress on the relaxational mode which lies in the lowest wavenumber region. For 11 simple organic liquids at room temperature, the relaxation time τ was obtained and also the parameter β which represents the distribution of τ; τ ranges from 1 to 5 ps. For toluene and tetrahydrofuran, the temperature evolution of the spectra was measured. It was found that τ of these liquids increases as the temperature is lowered. This is in harmony with the increasing viscosity with decrease in temperature. It was found that β is close to unity for most of the liquids studied, which implies a small distribution of τ in simple organic liquids.

Structural relaxations in amorphous biphenyl. Raman spectroscopic studies

Amorphous biphenyl films were prepared by vacuum evaporation onto cold metal substrates. Structural relaxations (SR) in the films were studied by in situ Raman measurements during annealing. Biphenyl molecules are twisted in the initial amorphous state as in the molten state. A gradual SR which causes increases in Raman-band intensities starts around 20 K. An abrupt SR occurs around 140 K irrespective of the initial temperature of the film preparation. These features of SR are discussed in comparison with those in amorphous p -terphenyl.

Ground state molecular pair formation in amorphous anthracene deposited onto a metal substrate at intermediate temperatures

Abstract Anthracene films deposited onto cold metal substrates in vacuum were studied by Raman spectroscopy. They were found to be amorphous but weakly indicated the formation of some molecular pairs with close contacts when the substrate temperature at deposition was set at around 120 K. Fluorescence measurements showed that these molecular pairs in the electronic ground state are the source of the previously reported excimer fluorescence. This local ordering in amorphous anthracene seems to inhibit the system from crystallization which starts at around 200 K if the sample is highly disordered.