The dielectric loss factor and dielectric permittivity of 8–16 mol% solutions of chlorobenzene, o-dichlorobenzene, and 1-chloronaphthalene in cis-decalin; 50–60 mol% mixtures of pyridine with chlorobenzene, bromobenzene, 1-chloronaphthalene, and toluene; 50–60 mol% mixtures of tetrahydrofuran with bromobenzene and 1-chloronaphthalene; the pure liquids cis-decalin, o-terphenyl, iso-propylbenzene, propylene carbonate; and two fused salt systems, 45 mol% Ca(NO3)2–KNO3 mixture and Ca(NO3)2·4H2O have been measured from 50 Hz to 1 × 105 Hz from − 196° in the vitreous state to about 30° above their respective glass transition temperatures. The Tg's of the organic glasses have been measured by DTA. With the exception of propylene carbonate, all glasses show the presence of one secondary relaxation between − 196° and their respective Tg's either as a peak or shoulder in a tanδ–temperature plot at a single frequency, or in the dielectric loss spectrum. Arrhenius plots of the frequency of maximum loss against temperature in the main relaxation region for all systems are nonlinear, with the activation energy at the lowest temperature of our measurements ranging from 55 kcal/mol to 70 kcal/mol. The Arrhenius plots in the secondary relaxation region are linear and have activation energies between 5 and 12 kcal/mol. These glasses, most of which are composed of rigid molecules, show a remarkable similarity in their dielectric behavior to amorphous polymers. The results confirm the prediction made by one of the authors that the occurence of secondary relaxations is an intrinsic property of the glassy state.

No abstract

The dielectric relaxation study of glass-forming liquids show the presence of two relaxation regions at temperatures above TQ. The low frequency relaxation is attributed to the cooperative rearrangement of molecules. The high frequency relaxation, which continues to exist in the glassy state, is suggested to arise from the hindered rearrangement of the molecules encaged by large regions which have been made relatively immobile by the stringent requirement of a cooperative motion. The hindered reorientation of dipoles in liquids at low viscosity has about the same Arrhenius energy as the β process seen in glasses. The results emphasize the role of intermolecular potential barriers in producing relaxation characteristics which have been generally accepted to arise from intramolecular rearrangement.

The thermal behavior of vapor-deposited amorphous solid water (ASW) was investigated by differential scanning calorimetry.After annealing in vacuo, ASW shows a thermally reversible glass-liquid transition: the onset temperature is 136 ± 1 K, the temperature range of the transition is ~14 deg, and the increase in the heat capacity is 1.9 ± 0.2 J K'1 mol™1. The heat of crystallization of the annealed ASW to cubic ice is -1.29 ± 0.01 kJ mol'1. These values are similar to those previously reported for hyperquenched glassy water. This similarity and the changes of the X-ray diffractograms feature indicate that ASW anneals or relaxes during heating in vacuo to a structural state approaching that of hyperquenched glassy water. Therefore, its state can be thermodynamically continuous with that of water, but its H-bonded structure is not likely to be the same as that of water at ambient temperature.

The amplitude of the orientational dielectric dispersion of impure polycrystalline ice Ih has been measured at temperatures down to 133 K in an attempt to find evidence for an ordering transition. The Curie–Weiss temperature is 6.2±1.7 K and so, within the experimental precision, there is no significant evidence that the molecular orientations become more correlated than the ice rules require. From the most recent results on polycrystalline ice, the Curie–Weiss temperature is 15±∼11 K. As this temperature is far below the lowest experimental temperatures, the evidence for an ordering temperature is not firm. The activation energy for dielectric relaxation in the impure ice is 25.5 kJ mol−1 at high temperature and increases at low temperatures. The low activation energy is caused by impurities that generate orientational defects in about the maximum number physically possible, and is mainly the activation energy for diffusion of the defects. At lower temperatures, the impurities produce fewer defects and the activation energy rises because the energy required to produce the defects begins to contribute to it. The low-temperature region in D2O ice with unknown dopants, which has been well studied by Johari and Jones and by Kawada, is due to this effect. An analysis suggests that the low-temperature region would be well worth studying for a sample with known dopants.

No abstract

Annals New York Academy of Sciences 0.05 17.2 mole % Chlorobenrene -c&-Decalin 0.01 tan 6 0.005 0.001 80 90 100 110 120 130 140 150 T /OK t FIGURE 1. The dielectric loss factor, tan 6 , of 17.2 mole% chlorobenzene/cis-decalin mixture at 1 k H z plotted against temperature, showing the temperature of the a and /3 relaxation peaks.quency. One maximum occurred at a temperature above the glass transition and the other, which was 1-2 orders of magnitude lower, occurred at several tens of degrees below the glass transition temperature Tg. A typical plot showing the two maxima is given in FIGURE 1, where tan 6 of 17.2 mole% solution of chlorobenzene in cis-decalin is plotted logarithmically against temperature at 1 kHz. Dilute solutions of halogen-substituted benzenes and naphthalenes in nonpolar solvent, cis-decalin,2 approximately 40 mole% mixtures of toluene, substituted benzenes and naphthalenes in pyridine2 and in tetrahydrofuran, pure liquids, e.g., isopropylbenzene,2 o-terphenyl,2 methyl-substituted h e p t a n o l~,~ dialkyl p h t h a l a t e~,~ insulating calcium nitrate tetrahydrate, and glucose-water mixtures of several compositions: all showed similar peaks in tan &temperature plots.The peak a t temperatures below Tg could not be detected in a few substances, namely in a mixture of chloronaphthalene in tetrahydrofuran,2 propylene carbonate,2 i~o -b u t a n o l ,~ I ,2-pr0panediol,~ 45 mole% Ca(NO3),KNO3,* and in glycerol,6 but the secondary relaxation could be clearly seen in a plot of tan 6 against the logarithm of frequency at temperatures below Tg in the chloronaphthalene-tetrahydrofuran mixture.2 The secondary relaxation could be clearly observed also in glycerol on the application of a few kilobam6 In other substances J o h a r i et al.: Molecular Liquids and Crystals 119 \ I / \ -/ \ / \ , / , I , \it can probably be either detected at high pressures or resolved (although less convincingly) bv a suitable analytical method as in ice.7 Without implying a similarity in their molecular mechanisms to the loss peaks seen in amorphous polymers, the relaxation observed above Tg is referred t o here as a relaxation and that observed immediately below Tg as p relaxation.The spectral features of the two relaxations were quite apparent. In the majority of substances, the plots of t " against the logarithm of frequency for a relaxation were asymmetric and had a half-width of 2-3 decades of frequency, which is many times higher than 1.40 decades for a single relaxation time. The frequency of 12 1 0 8 -w 6 PI1 4) 4 2 0 4 3 t W U 4) 2 I 0 17.2 molr % chlorobmronrcia-drcalln d ,' \ \ FIGURE 2. The dielectric loss c'' of 17.2 mole "/, chlorobenzenelcis-decalin mixture plotted logarithmically against frequency at 139.9"K ( 0 ) and 122.1"K ( 0 ) . The top curve is the (Y relaxation and the bottom curve the p relaxation region. The dashed curves are for a Debye-type single relaxation time. Johari et al.: Molecular Liquids and Crystals 34 mole % I-CHLORONAPHTHALENE-121 73 83 93 103 113 123 133 143 153 TEMPERATURE / O K FIGU...

Theory of relaxation in viscous liquids and glasses J. Chem. Phys. 81, 954 (1984); 10.1063/1.447697Viscous liquids and the glass transition. VI. Relaxations in simple molecule glasses in the 4-77 K range CONCLUSIONS ACKNOWLEDGMENTThe efg tensor resulting from a spanning of the T?g or the Eg subspace by real coefficients displays, remarkably, a constant electric quadrupole splitting and a variety of values of V .. and 7/. None of this information is present in the usual M ossbauer spectrum. Magnetic perturbation, or perhaps other techniques such as oriented single crystals, is required for the extraction of information relative to structure and bonding.The dielectric permittivity and the dielectric loss factor of 5-methyl-3, 4-methyl-3 and 3-methyl-3heptanol, n-and iso-butanol, 1,2-propanediol, dimethyl and diethyl phthallate, and 3-methylpentane have been measured from 50 to 105 Hz and from -196 to about 20°C above their respective glass transition temperatures. The glass transition temperature T. of these substances, several more isomeric octanols, and 1-phenyl-1-propanol have been measured by differential thermal analysis. All substances except for 3-methylpentane and iso-butanol show either a well-defined secondary relaxation peak in tan~, or a clear indication of the presence of a secondary relaxation below their To's. Arrhenius plots for the a-relaxation process of the isomeric octanols are linear with an activation energy of 16--18 kcal/mole, while for other substances they are nonlinear with the activation energy changing from 30 to 70 kcal/mole. The Arrhenius plots for the secondary relaxations are linear and have an activation energy of 4-8 kcal/mole. It is pointed out that the presence of a spectrum of relaxation times in liquids near T. is not necessarily concomitant with non-Arrhenius behavior. It is concluded that the presence of secondary relaxations should be considered as a characteristic property of the liquid in or near the glassy state, and do not require specific intramolecular mechanisms for their existance.