Activation energy mechanical relaxation

DMA Frequency response analysis (single or multiple frequencies) Mechanical strength and energy loss Storage modulus Loss modulus Loss factor Activation energies of relaxations Free-volume ratio (thermal expansion coefficient)... 

Using this expression and taking into account the approach adopted, it is possible to experimental data on changes in the mechanical loss factor (tangent of mechanical losses) overtime, the impact loads to find the estimates of the activation energy of relaxation process, determine the extent to which the process is stationary (steady), the degree of linearity of the... 

The dynamic mechanical properties of PTFE have been measured at frequencies from 0.033 to 90 Uz. Abmpt changes in the distribution of relaxation times are associated with the crystalline transitions at 19 and 30°C (75). The activation energies are 102.5 kj/mol (24.5 kcal/mol) below 19°C, 510.4 kJ/mol (122 kcal/mol) between the transitions, and 31.4 kJ/mol (7.5 kcal/mol) above 30°C. 

There remains an interpretation of ta to be found, ta exhibits an activation energy of about 0.43 0.1 eV, about three times as high as the C-C torsional barrier of 0.13 eV. The discrepancy must reflect the influence of the interactions with the environment and therefore ta appears to correspond to relaxation times most likely involving several correlated jumps. The experimental activation energy is in the range of that for the NMR correlation time associated with correlated conformational jumps in bulk PIB [136] (0.46 eV) and one could tentatively relate ta to the mechanism underlying this process (see later). 

Fig. 5.16 Q-dependence of the characteristic times of the KWW functions describing the PIB dynamic structure factor at 335 K filled circle), 365 K empty square) and 390 K filled triangle), a Shows the values obtained for each temperature. Taking 365 K as reference temperature, the application of the rheological shift factor to the times gives b and a shift factor corresponding to an activation energy of 0.43 eV delivers c. The arrows in a show the interpolated mechanical susceptibility relaxation times at the temperatures indicated. (Reprinted with permission from [147]. Copyright 2002 The American Physical Society)...

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