Itaru Tsukushi

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.

CALORIMETRIC STUDY OF ETHYLENE GLYCOL AND 1,3-PROPANEDIOL : CONFIGURATIONAL ENTROPY IN SUPERCOOLED POLYALCOHOLS

Abstract The heat capacities of crystalline, liquid, supercooled liquid, and glassy states of ethylene glycol (EG), and 1,3-propanediol (PD) were measured with an adiabatic calorimeter in the temperature range between 13 and 300xa0K. The glassy ethylene glycol was prepared by quenching of a liquid sample doped with about 5% of glycerol to suppress crystallization. The effect of the doping on thermodynamic quantities was corrected for by assuming the additivity of the heat capacities of ethylene glycol and glycerol. The configurational entropy S c was calculated for EG, PD and several other alcohols using the present and literature data. The temperature dependence of S c for the supercooled-liquid polyalcohols was well reproduced by a model which assumes that all the hydroxyl groups are engaged in hydrogen bonds and that the configurational entropy is governed by the reorientation about the C–C or C–O single bonds and OH⋯O hydrogen bonds. The relation between the configurational entropy and the structural relaxation times is discussed in the framework of the Adam–Gibbs theory and Vogel–Tammann–Fulcher equation.

Solid state amorphization of organic molecular crystals using a vibrating mill

Abstract The solid-state amorphization of organic molecular crystals was studied by differential scanning calorimetry (DSC) and X-ray powder diffraction. Two clathrate compounds of tri- O -methyl-β-cyclodextrin (TMCD) containing p -nitrobenzoic acid (NBA) and p -hydroxybenzoic acid (HBA), and seven other organic compounds, sucrose (SUC), salicin (SAL), phenolphthalein (PP), 1,3,5-tri-α-naphthylbenzene (TNB), p -quaterphenyl ( p -QP), p -terphenyl ( p -TP) and 1,3,5-triphenylbenzene (TPB) were ground for 2–16 h with a vibrating mill at room temperature. A halo diffraction pattern and exothermic effect due to the crystallization were observed in TMCD-NBA, TMCD-HBA, SUC, SAL, PP and TNB, indicating amorphization of these crystals. The ability of solid-state amorphization in organic molecular crystals was discussed from a thermodynamic point of view.

Boson peaks of glassy mono- and polyalcohols studied by inelastic neutron scattering

We have measured the inelastic neutron scattering spectra of the glasses of six mono- and polyalcohols; 1-propanol, ethylene glycol, propylene glycol, 1,3-propanediol, glycerol and threitol. Broad excitation peaks with peak top energy of 3-5 meV appeared in all of the S(2θ,E) spectra. These peaks were identified as boson peaks characteristic of glassy materials from the temperature dependence of the peak intensity. We found a systematic relation among the boson peak energy, the boson peak intensity per molecule and the hydrogen-bond density estimated as the ratio of the number of hydroxyl groups to that of carbon atoms (NOH/NC); the peak energy decreases and the peak intensity increases as hydrogen-bond density decreases. The present result indicates that the origin of the boson peak in network glasses is related to the flexible part in the network structure (e.g., non-hydrogen-bonded alkyl-groups in alcohol glasses). We also measured partially deuterated propanol (CD3CD2CD2OH and CH3CH2CH2OD) and glycerol (CD2(OH)CD(OH)CD2OH and CH2(OD)CH(OD)CH2OD). Both energy and intensity of the boson peak were not affected much by the partial deuteration, indicating that the hydrogen-bonding and non-hydrogen-bonding (alkyl) parts contribute to the boson peak cooperatively. The present result was compared with the predictions from a simple model recently developed by Nakayama et al.

Inelastic neutron scattering study of low-energy excitations in vapor-deposited glassy propylene

We have developed a novel cryostat in which glassy states of molecular substances are formed by deposition of their vapor on a cold substrate. The glassy samples are subjected to in situ inelastic neutron scattering experiments. By the use of this cryostat, the glassy state of propylene(CH2=CHCH3) prepared at 20 K was examined on an inverted geometry time-of-flight neutron spectrometer in the energy range below 10 meV. The measurement was performed also on the glassy sample annealed at the glass transition temperature (55 K). A broad excitation peak (boson peak) was found at around 3 meV in the S(2θ,ω) spectra of the as-deposited and annealed samples. The absolute densities of vibrational states G(ω) were derived by combining the neutron spectra and the heat capacity data of a similar compound 1-butene (CH2=CHCH2CH3). The number of vibrational modes associated with the low-energy excitation was 1.64 per molecule for the as-deposited sample and 1.34 for the annealed sample. The boson peak energy depends on...

Heterogeneity of amorphous polymers with various fragility indices as studied in terms of non-Gaussian parameter

Abstract Dynamical heterogeneity of amorphous polymers has been studied in terms of non-Gaussian parameter, A0. This parameter was estimated as a function of temperature, time, and fragility of polymers using the incoherent elastic neutron scattering technique. We found that the heterogeneity of the amorphous polymers increases with decreasing temperature, especially below the glass transition temperature and also that the stronger (or less fragile) polymers are more heterogeneous.

Solid state amorphization and glass transition of tri-O-methyl-β-cyclodextrin

Amorphous solid of tri-O-methyl-β-cyclodextrin was formed by grinding the crystalline sample with a vibrating mill at room temperature. The amorphising process was examined by X-ray powder diffraction technique and differential scanning calorimetry (DSC). The Bragg peaks disappeared and the enthalpy of crystallization became constant for the sample ground for 25 min, indicating the apparent completion of the amorphization. A glass transition of the ground amorphous solid was found by DSC. The glass transition temperature Tg moved from 58°C to 79°C with grinding. The saturated Tg of the ground sample was the same as that of the liquid-quenched glass. No significant difference between the ground and liquid-quenched amorphous solids was found in the X-ray diffraction patterns. Infrared spectra of both amorphous solids, however, showed a definite difference for the band at 1194 cm−1 assigned to the rocking of the CH3 groups which are located at the molecular periphery.ZusammenfassungAmorphes festes Tri-O-methyl-β-cyclodextrin wurde bei Raumtemperatur durch Mahlen einer kristallinen Probe in einer Vibrationsmühle hergestellt. Der Amorphisierungsprozeß wurde mittels Röntgenpulverdiffraktion und DSC verfolgt. Die Braggschen Peaks verschwanden und die Kristallisierungsenthalpie nahm nach einem Mahldauer von 25 min einen konstanten Wert an, was auf die augenscheinliche Beendigung des Amorphisierungsprozesses hinweist. Mittels DSC wurde ein Glasumwandlungspunkt des gemahlenen amorphen Feststoffes gefunden. Die Glasumwandlungstemperatur Tg stieg durch das Mahlen von 58°C auf 79°C. Der Sättigungswert Tg der gemahlenen Probe war der gleiche wie für flüssigkeitsabgeschrecktes Glas. In den Röntgendiffraktogrammen konnte zwischen den gemahlenen und den flüssigkeitsabgeschreckten amorphen Feststoffen keinen Unterschied feststellen. Die IR-Spektren von beiden amorphen Feststoffen zeigen einen signifikanten Unterschied für die Bande bei 1194 cm−1, der Nickschwingung der CH3-Gruppen am Molekülrand.

A calorimetric study on the configurational enthalpy and low-energy excitation of ground amorphous solid and liquid-quenched glass of 1, 3, 5-tri--naphthylbenzene

An amorphous solid of 1, 3, 5-tri--naphthylbenzene (TNB) was prepared by grinding the crystalline sample with a vibrating mill. Heat capacities of the ground amorphous solid (GAS), liquid-quenched glass (LQG) and crystal of TNB were measured with an adiabatic calorimeter in the temperature range 10 - 330 K for the GAS and 5 - 370 K for the LQG and crystal. The heat capacities of the LQG and GAS were 0.5 - 1% larger than that of the crystal. The heat capacity of the GAS agreed with that of the LQG between 30 and 330 K but was 1 - 4% larger than that of the LQG below 30 K. The heat capacity difference in the low-temperature region can be attributed to the difference in low-energy excitation which is known as a universal property of amorphous materials. A glass transition occurred at 342 K for the LQG. For the GAS, however, a large exothermic effect due to crystallization appeared from 315 K, which is 25 K lower than of the LQG. The configurational enthalpy of GAS determined from the enthalpy of crystallization was much larger than that of the LQG. This result indicates that the structure of the GAS is much more disordered and strained than that of the LQG.

Excess heat capacities due to the low-energy excitations of molecular glasses: An approach using the soft potential model

We have investigated the low-temperature heat capacities arising from the low-energy excitations in several molecular glasses. The heat capacities of glassy toluene, ethylbenzene, and 3-methylpentane were measured with an adiabatic calorimeter. The first two samples were doped with 10 molu2009% of benzene to prevent crystallization. The low-temperature heat capacities of the molecular glasses measured in this study and those measured previously were all reproduced well by the sum of a normal part represented by the Debye function and an excess one represented by the soft potential model. The peak energy of G(ω)/ω2 [G(ω): density of states, ω: energy] was found to be proportional to M−1/2 (M: molecular mass) for the hydrocarbon molecules but not for the alcohol molecules. Intermolecular hydrogen bonds in the alcohols may be responsible for the different behavior.

Solid-state formation and amorphization of the inclusion compound tri-O-methyl-β-cyclodextrin-benzoic acid

Abstract Differential scanning calorimetry (DSC), X-ray powder diffraction, and IR spectroscopy of a 1:1 inclusion compound of tri- O -methyl-β-cyclodextrin (TMCD) and benzoic acid (BA) were carried out. About 75% of the inclusion compound was formed by shaking an equimolar physical mixture of TMCD-BA for 180 min. The X-ray diffraction pattern of the inclusion compound formed was almost the same as that of the pure TMCD crystal. The inclusion reaction was completed by grinding for 3 min with a vibrating mill. Further grinding for 40 min transformed all the inclusion crystals into an amorphous state, whose X-ray diffraction pattern is similar to that of a liquid-quenched glass. A glass transition was observed in the temperature range of 58–64°C. The grinding-time dependence of the T g was almost the same as that of the pure TMCD, i.e. the T g increased with grinding and approached that of the liquid-quenched glass. The amorphous TMCD-BA inclusion compound crystallized at around 80°C into a metastable phase, which has an entropy smaller than that of the stable phase. The metastable phase then underwent an irreversible transition to the stable phase at around 100°C with an endothermic effect. The stable crystalline modification fused at 174°C.