The Shock-Wave Method

Alongside the acoustic methods of measuring relaxation times at lower temperatures, the shock-wave method has also widely been used. 

Assuming that the equiHbrium distribution of translational and rotational energy sets in virtually instantaneously just behind the shock front, use can be made of the conservation equation for mass, linear momentum and energy to express the translation-rotational temperature Tj and density pi just behind the shock front in terms of these quantities Tq and po ahead of the front. 

at a time t, when the vibrational relaxation starts to proceed behind the shock front, the same equations describe the evolution of the mean vibrational energy Eyib and the translation-rotational temperature T in terms of density p. 

After a certain time the relaxation process is completed behind the shock front, leading to a certain temperature Tg and to the corresponding equilibrium vibrational energy Eyib,2 = Evib(T2). 

The vibrational relaxation time is obtained by measuring either p(t) or Eyib in the course of relaxation and using the expression 

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The plots are significantly curved, especially at high temperatures. The authors have been able to compare these plots with experimental data taken from various sources, each in a different temperature range. This includes the authors own results (31) on the reaction between H2 and CH s, obtained by the shock-wave method. The agreement is quite close in particular, the points obtained experimentally at temperatures above 1000 K lie way above the straight line extrapolated from the low-temperature results. The tunnel effect was taken into account in these calculations (see Section VLB) but does not seem to affect the plot appreciably. The authors calculate the activation parameters which best fit their calculated curves, and find dEajdT to be higher than predicted by the classical limit of the partition functions. 

In Sect. 3.3.3, a peculiar dynamics in the hybrid PU-PHEMA semi-IPNs was discussed. In the work described in [239,240], a series of PU-PHEMA-ND nanocomposites with different matrix compositions and ND contents of 0.25, 1, or 3 wt% were studied. Their nanostructure, glass transition dynamics, and elastic properties were investigated in the combined CRS/AFM/DSC experiments. We revealed a possibility of large and specific impact of low content of 3D nanofiller on polymer matrix, without performing a special functionalization of its surface. For preparing nanocomposites, the NDs obtained by the shock-wave method, with the particle sizes of 2-lOOnm and specific surface area of 220m g were used. NDs were introduced into the reaction mixture at the stage of PU synthesis. 

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