Syuzo Seki

Thermodynamic investigation on glassy states of pure simple compounds

Abstract The present review deals primarily with glass transition phenomena in pure simple compounds and pays special attention to the thermodynamic aspects of the vitrification process. The concept of glassy state is extended to liquid crystalline and even to crystalline materials which have any type of disorder. Thus the familiar supercooled liquid-glass transition is shown to be just one example of a class of ‘glass transitions’ due to loss of equilibrium which must occur quite frequently in condensed matter. Evidence of several glass transition phenomena in one and the same compound is given. The fact that glass should be considered as one of the states of aggregation of matter, irrespective of either the method of formation or the existence of three-dimensional periodicity in molecular arrangements, is stressed.

Calorimetric study of the glassy state X. Enthalpy relaxation at the glass-transition temperature of hexagonal ice☆

Abstract Heat capacities of hexagonal ice were measured with an adiabatic calorimeter. Anomalous temperature drifts and the corresponding C s T hump were observed around 100 K. The sample was then annealed at constant temperatures between 85 and 110 K and the spontaneous temperature change during the annealing was followed. The anomalies were found to be dependent upon the annealing conditions. This thermal behavior is quite similar to that of a glass around the glass-transition temperature. If these phenomena are regarded as the initiation of the proton-ordering process, the configurational entropy change down to 89.4 K, configurational entropy for completely disordered pattern, (3.41 ± 0.22) J K−1 mol−1, and activation enthalpy for the ordering process, (22±4) kJ mol−1, are obtained.

Calorimetric study of the glassy state XII. Plural glass-transition phenomena of ethanol

Abstract Ethanol was found to give a metastable crystalline phase (crystal-II) when the liquid was cooled at a moderate rate. Glassy states of liquid and of newly found crystal-II were obtained in the calorimeter cell by controlling the cooling rate of the liquid. The heat capacities of these phases as well as that of the stable crystal-I were measured by an adiabatic calorimeter in the temperature range between 14 and 300 K. The glass transition temperature T g , the heat-capacity jump at T g , and the residual entropy were found to be 97 K, 35.3 J K −1 mol −1 , and 8.93 J K −1 mol −1 for the glassy liquid, and 97 K, 22.8 J K −1 mol −1 , and 4.24 J K −1 mol −1 for the glassy crystal-II, respectively. The values for the residual entropy are referred to the third-law entropy for crystal-I. The heat capacities reported previously for the supercooled liquid by Gibson et al. and by Parks and Kelley agree well with those for the metastable crystal-II. Those of the supercooled liquid connect smoothly with those obtained for the liquid above the melting temperature. Thus, ethanol is found to be another example of a low-molecular-weight compound which shows multiple glass-transition phenomena.

Heat Capacity of [Cr4(OH)6(en)6](SO4)3·10H2O from 1.4 to 200 K and Spin Interaction

The heat capacity was measured between 1.4 and 200 K. The magnetic contribution was determined by subtracting the lattice contribution from the overall heat capacity with the aid of effective frequency distribution function. The magnetic heat capacity showed two peaks at 2.3 K and at about 20 K. These features are satisfactorily accounted for by assuming a spin Hamiltonian of the form, \(\mathscr{H}{=}-J(\textbf{\itshape S}_{1}{\cdot}\textbf{\itshape S}_{3})-j[(\textbf{\itshape S}_{1}{\cdot}\textbf{\itshape S}_{2})+(\textbf{\itshape S}_{2}{\cdot}\textbf{\itshape S}_{3})+(\textbf{\itshape S}_{3}{\cdot}\textbf{\itshape S}_{4})+(\textbf{\itshape S}_{4}{\cdot}\textbf{\itshape S}_{1})]-J_{24}(\textbf{\itshape S}_{2}{\cdot}\textbf{\itshape S}_{4})\). The closest agreement between theory and experiment was obtained for J =-42.6 k , j =-22.8 k and J 24 =-7.6 k . The sign of the parameters indicates that all the spin interactions are antiferromagnetic. It was concluded that one need not introduce any higher-order ...

Heat Capacities and Volume Thermal Expansion of NaNO2 Crystal

Phase transitions of ferroelectric NaNo 2 crystal around 164°C were studied by calorimetric and dilatometric methods. The values of both heat capacity and molar volume show an abrupt increase at about 163°C, indicating that this transition is of the first order. In the region of 164∼165°C, a small broad peak was observed in the C p – T curve. On the other hand there appear two small anomalies in the volume expansion curve at 164.2°C and 164.7°C respectively. The total entropy of transition amounts to 1.26±0.08 e. u., which is nearly equal to R 1n2=1.377 e. u., and suggests that the orientational order of NO 2 - ions is destroyed completely in the paraelectric phase.

Heat Capacity of N-(o-Hydroxy-p-Methoxybenzylidene)-p-Butylaniline: A Glassy Nematic Liquid Crystal

Abstract The heat capacity of N-(2-hydroxy-4-methoxybenzylildene)-4′-butylaniline(2,4-OHMBBA) with a purity of 99.393 mole % was measured between 13 and 375 K. The Melting point T m was 314.30 K, and the enthalpy and the entropy of fusion were 22.405 kJ mol−1 and 71.425 J K−1 mol−1, respectively. The temperature of transition from nematic to isotropic liquid was 33.65 ± 0.1 K, and the enthalpy and the entropy changes due to this mesophase transition were 887.4 ± 4.9 J mol−1 and 2.690 ± 0.015 J K−1 mol−1, respectively. A second-order character has been postulated for the mesophase transition. By cooling the nematic liquid crystal at a rate of − 12.2 K min−1 a frozen-in state of the stable nematic phase, i.e. a glassy state, was realized. The glass transition temperature Tg was 204 K and the heat capacity jump at T g was Δ C = 107 J K−1 mol−1. The activation enthalpy for the glass transition was estimated to be Δ H = 75 kJ mol−1. The residual entropy of the glassy state at O K was determined to be 12.69 ± 0...

Dielectric Relaxations in Various Crystal Modifications of Cyclohexanol and 2,3-Dimethylbutane

Abstract The dielectric constant and loss of crystalline cyclohexanol (CHOL) and 2,3-dimethylbutane (DMB) were measured from 4°K to the melting point, 299°K for CHOL and 145°K for DMB. The supercooled plastic crystal of CHOL above the glass temperature Tg exhibits a prominent relaxation (α) due to molecular rotation. The temperature dependence of therelaxation time was found to obey the Fogel-Tamman equation. A secondary relaxation (β) was observed below Tg , 149°K for CHOL and 76°K for DMB. The mechanism proposed for β is internal rotation; rotationof OH bond for CHOL and trans-gauche transformation for DMB. The β relaxation of DMB is well correlated with acoustic relaxation in the liquid state in the relaxation time versus timperature plot. Relaxations in the intermediate state, crystal III, of these two substances and the most stable state, crystal II of DMB were studied.

Magnetic and Thermal Properties of Crystals Including Isolated Clusters. I. Heat Capacity and Infrared Spectrum of [Cr3O(CH3COO)6(H2O)3]Cl·6H2O Crystal between 1.5 and 280 K

The heat capacity was measured between 1.5 and 280 K. At liquid helium temperatures a heat capacity anomaly was observed and a new phase transition was found at 211.4 K with a secondary C p maximum at 215.5 K. The entropy and the enthalpy changes for the overall transition are Δ S t =13.778 J K -1 mol -1 and Δ H t =3322 J mol -1 , respectively. The infrared spectra were measured at 120,225 and 295 K. Many new absorption peaks appeared below the transition point. A mechanism for the phase transition is suggested in terms of ordering processes of crystalline water. A new model is proposed for explaining the heat capacity anomaly at liquid helium temperature: The cluster ions with equilateral triangle symmetry at room temperature are slightly distorted through the phase transition processes resulting two kinds of cluster ions forming isosceles triangles with different exchange parameters. The closest agreement with the experimental data was obtained by assuming J 0 =30 k and J 1 =4.5 k for half moles of the ...

Phase Transitions in the Quinol Clathrate Compounds. I. The Quinol Hydrogen Cyanide Clathrate Compound

The heat capacity of the clathrate compound of quinol with hydrogen cyanide was measured from 12 to 300 K. It exhibited a well defined anomaly at 177.8+0.1 K. The entropy change associated with it was estimated to be 5.71±0.3 J/mol K. This value is close to Rln2, implying that the anomalous heat capacity is due to the order-disorder phase transition concerned with the orientation of the trapped molecules. Dielectric study supported this view. Far infrared spectra of the crystal was recorded from 38 to 500 cm -1 over a range of temperature. Two bands at 46 and 95 cm -1 were found to be characteristic of this substance. A possible assignment of the former band was proposed. Finally, the lattice sum calculation showed that the dipole interaction energy between the guest molecules corresponds to 318 K of temperature compared with the observed transition temperature.

Self-Diffusion in Some Plastic Crystals

Abstract Self-diffusion phenomena in several plastic crystals were studied by use of high-resolution n.m.r. techniques which have been hither to applied to pure liquid or solution systems. The pursuit of spectral narrowing processes, with the aid of Kubo-Tomita formula, makes it possible to evaluate the kinetic aspects of diffusional motion. Activation enthalpies for diffusion were obtained for trimethylacetic acid, triethylenediamine, succinonitrile and ammonium nitrate; they were 8.09 ± 0.25, 21.7 ± 1.0, 10.7 ± 0.5 and 11.3 ± 0.5 kcal/mole, respectively. These data, as well as those available for the other plastic crystals, were correlated with the latent heat of fusion in a similar manner to those for cubic metals. Also, the chemical shift of OH resonance relative to CH3 resonance line of trimethylacetic acid was measured for the crystal and liquid phases. Temperature coefficient of OH chemical shift is of the order of 1.0 × 10−2 ppm/°C. This observation and the other evidence suggest strongly the vali...