Sample temperature relaxation

Sample (B), relaxed a-form, prepared by allowing the strained sample to warm to room temperature and so relax back to a-form material. 

In the time constant (relaxation) method, the waveform of P is a negative step which produces a relaxation of the sample temperature from TB + ST to TB. The measure of P(T) may be critical when the power P is comparable with the spurious power or when the thermal conductance G is steeply variable with the temperature (i.e. G oc T3 in the case of contact conductances). 

Finally, we should mention the sample temperature control. It is a direct consequence of all relaxation theories that, in any FFC NMRD application. 

The procedures for recording spectra of heteronuclei often differ considerably from those for H and (which would today be considered routine ) since it is necessary, even for routine measurements, to adjust the experimental conditions to suit the special properties of the nuclei to be observed. For example, the spin-lattice relaxation times for some nuclides, such as N, are very long, whereas for others (especially those with an electric quadrupole moment, such as N) they are very short. Also, the spectra observed for some nuclides contain interfering signals caused by other materials present, for example the glass of the sample tube ("B, Si), the spectrometer probe unit ( Al) or the transmitter/receiver coil. For many nuclides the sample temperature and its constancy are important factors for example, quadrupolar nuclides such as O give narrower signals when the temperature is increased. 

If the excitation occurred at a low temperature such that the thermal emission rate of carriers from traps is very small, the perturbed equilibrium will exist for a long time and only upon an appropriate increase of the sample temperature can the relaxation process proceed at a rate that permits one to monitor it by measuring the conductivity a(T) = exp(ncfin + Pl p) of the sample (TSC) or the luminescence (TSL) emitted by radiative recombination of carriers thermally released from the traps. 

Nuclear Magnetic Resonance (NMR) Spectroscopy. Longitudinal and transverse relaxation times (Ti and T2) of 1H and 23Na in the water-polyelectrolytes systems were measured using a Nicolet FT-NMR, model NT-200WB. T2 was measured by the Meiboom-Gill variant of the Carr-Purcell method (5). However, in the case of very rapid relaxation, the free induction decay (FID) method was applied. The sample temperature was changed from 30 to —70°C with the assistance of the 1180 system. The accuracy of the temperature control was 0.5°C. 

The high-temperature relaxation process is typical for amorphous polymers and can be assigned to the a-relaxation that appears in the whole frequency range and in the temperature interval from 50 to 100°C. This process is well observed for all samples. It corresponds to the glass-rubber transition of the amorphous phase. 

Er The relaxed permittivity, equal to the bulk permittivity when molecular dipoles align with the electric field to the maximum extent possible at the sample temperature. 

Recently a relaxation method [6,7] has been developed to measure Cp at very low temperature. As the method can change a sample temperature rapidly due to the use of a very small amount (5-30 mg) of sample for the measurement, the Cp values at the temperature can be determined rapidly and precisely from near absolute zero to 400 K [8-14]. In the present study, we have attempted to determine the y values of the intermetallic compounds of the Mg-Zn binary system by using the relaxation method. 

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,... 

Figure 7 Absorption frequency (Q-branch) vs. temperature for the CO asymmetric stretch of W(CO)6 in the gas phase. A representative error bar is shown. Extrapolation to 450 K (internal vibrational temperature following relaxation of the 2000 cm-1 CO stretch) yields a temperature-dependent shift of 1.1 cm" 1 from the peak position at 326 K, the initial sample temperature.

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. 

In describing this effect as an avalanche excitation mechanism, it is clear that the details of the process differ from those of the Photon Avalanche described in Sect. 9 since,being ultimately a single-ion effect, this mechanism does not involve runaway cross relaxation as an essential step, but is instead intimately related to temperature effects. Within the avalanche formalism, this mechanism is best described as a thermal avalanche, in which high excitation powers result in runaway sample heating rather than runaway cross relaxation. This mechanism is illustrated schematically in Fig. 17 a. The dashed fines in Fig. 17 a show the isothermal excitation behaviors for two internal sample temperatures, and... 

Viscosity. Many ILs are highly viscous, especially in pure form. For these samples, strong relaxation leads to relatively broad signals. Apart from lowering the viscosity, e.g., by raising the sample temperature, not much can be done about this. 

Vittadini et al., (2001) investigated the media systems further with the proton decoupled NMR relaxation rate measurement using a 300 MHz NMR spectrometer (Bruker MSL 300) with a WALTZ pulse sequence. Acquisition parameters were 41 ms acquisition time, 9 /rs 90° pulse width, 100 ms recycle delay and 32°C sample temperature. Transverse relaxation rate Rz) was analyzed from line shape analysis after the system was... 

For all of the applications outlined above, and many others besides, it is desirable to use NMR parameters which possess an intrinsic temperature dependence in order to measure directly the sample temperature. These measurements can either be performed as a pre-experiment calibration procedure using identical data acquisition parameters as for the actual experiment, or as an in situ measurement using the actual sample. Temperature-dependent NMR parameters include spin lattice (Ti) and spin-spin T2 relaxation times, chemical shifts, dipolar and scalar couplings, molecular diffusion coefficients and net equilibrium polarization. Dependent upon the particular application, each of these parameters has been utilized as an NMR thermometer . 

The BCB exhibits minimal solid-like character upon heating contraction due to solvent evaporation only slightly outpaces thermal expansion. The Tg remains significantly below the sample temperature, resulting in a low modulus and thus low stress. Upon reaching 260°C, the tensile stress in the BCB film relaxes because of only minimal network formation, which would inhibit the relaxation, during the heating cycle. 

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