Low temperature relaxation

Giant field dependence of the low temperature relaxation of the magnetization in a dysprosium(III)-DOTA complex. Chem. Commun., 47, 3751-3753 (b) Cucinotta, G., Perfetti, M., Luzon,... 

According to a dynamic mechanical study by Saba, Sauer, and Woodward (1963) for PPO and a dilatometric study by Daane and Barker (1964) for cellulose acetate, the high-temperature relaxations of PPO, CDA, and CTA are primary relaxations which arise from segmental motion in the amorphous phase and the low-temperature relaxations are presumably ascribed to a more local motion in the amorphous phase. 

The behavior of the low-temperature relaxation of PMLG seems to be well explained by the two-phase model theory described in 4.4. In this relaxation, d"/d is positive and, since the mechanical loss tangent E"/E is larger than d"/d e"/e is negative in accordance with the inequalities (100) and (101). 

In conclusion, one cannot but state, that the present-day knowledge of the mechanism of the low-temperature relaxation of polyethylene remains limited and qualitative, even though theoreticians have mainly studied this kind of molecular motion. The low-temperature relaxations of the other polymers without side chains are ascribed to analogous types of motion because the existing experimental data do not allow a better founded interpretation. 

In order to assess the orientational stability of the poled state, the temperature dependence of the dipole mobility of the side groups was examined through dielectric relaxation measurements. (13) No low temperature relaxation below Tg was observed in the frequency range studied (100 Hz-100 kHz). In addition, the dielectric constant was approximately equal to the square of the refractive index, indicating that below T only electronic and no significant orientational contributions to the dielectric displacement are present. Thus, it was expected that a given orientational state of the ensemble would be stable at temperatures significantly below Tg. 

In general, most polymers lose their ductile properties below the glass transition temperatures (Tg), the point at which the movements of polymer chain segments become extremely restricted. In amorphous polymers, the characteristics of the low temperature relaxations are directly related to the chemical structure and the dynamics of polymer chains. There are several possible types... 

The dynamic mechanical response of three 2,4-T-2P samples at 11 Hz is shown in Figure 7 for three hard-segment concentrations. A low temperature relaxation maximum, s, in the region of — 68° to — 54°C,... 

Complementary spin-lattice relaxation measurements corroborate the observations made using the 2H line-shape measurements. Based on these measurements the low temperature relaxation times are dramatically shorter in the intercalated sample as compared to the bulk, indicating enhanced polymer re-orientation dynamics in the intercalated samples. Furthermore, the temperature dependence of the relaxation time in the bulk and intercalated sample show dramatic differences. While the relaxation time for the intercalated sample passes smoothly from low to high temperatures, the bulk sample shows a break between the crystalline state and melt state, with the melt state relaxation times at least one order of magnitude faster than those observed in the intercalated sample at the same temperature. 

A brief review and reassessment of data on the photophysics of benzene has been presented by Pereira. Evidence for the l E2g valence state has been obtained by u.v. two-photon spectroscopy.Slow electron impact excites fluorescence in thin films of benzene at 77 K as well as emission from isomers." The fluorescence yields and quenching by chloroform of alkyl-benzenes and 1-methylnaphthalene after excitation into Si, Sz, and S3 states and after photoionization have been measured. The channel-three process has been reconsidered in terms of the effects of local modes and Morse oscillator potentials. Excited-state dipole moments of some monosubstituted benzenes have been estimated from solvent effects on electronic absorption spectra, Structural imperfections influence the photochemistry of durene in crystals at low temperatures. Relaxation time studies on excited oxido-substituted p-oligophenylenes have been made by fluorescence depolarization... 

F. Stillinger, Role of potential energy scaling in the low-temperature relaxation behavior of amorphous materials. Physical Review B 32 (1985), 3134... 

Early investigations of the effect of water on the low-temperature relaxations of several aromatic polymers including polycarbonate, polyamides, and a polyurethane have shown several low-temperature anomalies (A .5). the case of a water-saturated... 

THE LOW TEMPERATURE RELAXATION Although three different sample types are illustrated in Figure 2.12a and b (wet, dry, and dry annealed), let us focus on the dry annealed sample containing minimal moisture ( 0.1%). Above 80 °C, the temperature dependence is linear (Arrhenius), whereas below 80 °C it is non-Arrhenius. This shows... 

Low Temperature Relaxation The low temperature relaxation is highly influenced by moisture content in wet samples, the conductivity decreases as water evaporates, disguising the actual dielectric properties of CS above 100 °C, while for moisture contents lower than 3 wt% and higher than 0.5 wt% (dry films), a non-Arrhenius behavior appears. However, in dry annealed CS (moisture contents <0.05 wt%), this low temperature relaxation vanishes after the second heat treatment. 

LOU 97b] Lourdin D., Bizot H., Colonna P., Correlation between static mechanical properties of starch-glycerol materials and low-temperature relaxation , Macromolecular Symposia, vol. 114, pp. 179-185,1997. 

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