Dielectric loss spectra, polymers

In Figure 17 (curve 1), the dielectric loss spectrum for PS at room temperature as taken from Bur [18] is presented. There are no pronounced relaxation loss peaks due to a- and / -processes in this polymer which is considered to be nonpolar , although in fact it possesses a smaU dipole moment due to the asymmetry at the phenyl side group. The loss tangent is seen to be constant and relatively small over a very broad frequency range from subaudio to 10 Hz. A loss peak occurs at vs2 x 10 Hz, a very high frequency for Debye relaxation dispersion. It appears to be the 5-peak which has been n asured by McCammon et al. at 46 K (1 kHz) with an activation energy of 12 kJ mole" ... 

Fig. 4.21. Temperature-frequency contour map of the dielectric loss spectrum for (a) polymer I and (b) polymer III. (From Ref. 102 by permission of the publishers, Butterworth-Heinemann Ltd. )...

The dielectric loss relaxation spectrum e"( )/ was shown to be uniformly accurately described by EQxp(—aa> ) at smaller frequencies and ea> at larger frequencies. For a small 38 kDa poly(D,L-lactic) acid, the scaling parameters are substantially independent of c with a larger 119 kDa poly(D,L-lactic) acid, a increases with increasing c. The parameter S is often but not always equal to unity when 5 = 1, a is a true time. At elevated polymer concentration, the exponent x is smaller correspondingly, dielectric loss relaxation spectra become broader. 

Figure 6 Inversion of the dielectric loss data for the normal mode spectrum of the type-A polymer polyisoprene. In the inset, the dielectric loss data show the spectrum of normal modes and at higher frepuencies the segmental mode. The distribution of relaxation times shows peaks at times that are characteristic of the different normal modes. However, the obtained peak positions differ from the Rouse theory predictions (shown by vertical lines).

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