Dielectric relaxation in solid polymers

Several distinct relaxation processes are usually present in a solid polymeric material, and these are dielectrically active if they incur significant orientation of molecular dipoles. The multiplicity of relaxation processes is seen most easily in a scan of dielectric loss at constant frequency as a function of temperature (Fig. 3.6). As the temperature is raised, molecular mobilities of 

Detailed examination of the relaxations requires isothermal scans of relative permittivity and dielectric loss factor as a function of frequency/ so that effective dipole movements and activation energies of relaxation times may be obtained. A typical pair of plots of d and e values against log/is shown in Fig. 3.7. Graphs of dielectric data of this kind are sometimes called, rather 

Other complications may arise in dielectric relaxation spectra of polymers from chain branching, which may introduce a distinct relaxation process connected with molecular motion at a branch point, and from crosslinking, which greatly restricts certain kinds of molecular movement. 

Relaxation processes in solid polymers are summarised diagrammatically in Fig. 3.14. 

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Jonquieres, A. and Fane, A. 1998. Modified BET models for modeling water vapor sorption in hydrophilic glassy polymers and systems deviating strongly from ideality. J. Appl. Polym. Sci. 67 1415—1430. Jonscher, A.K. 1983. Dielectric Relaxation in Solids. London, U.K. Chelsea Dielectric Press. 

Williams, G. Molecular Aspects of Multiple Dielectric Relaxation Processes in Solid Polymers. Vol. 33, pp. 59—92. 

Wilkes, G. L. The Measurement of Molecular Orientation in Polymeric Solids. Vol. 8, pp. 91-136. Williams, G. Molecular Aspects of Multiple Dielectric Relaxation Processes in Solid Polymers. Vol. 33, pp. 59-92. 

Reorientation dynamics of molecular tracers in polymers is not only important for the understanding of slow relaxation phenomena in glassy polymers but plays also a critical role in practical problems such as molecular design of nonlinear optical materials with long-term stability based on dyes/polymers complexes. We show here the reorientation dynamics of molecular tracers in glassy polymers obtained by the armealing-after-irradiation method described below. These experimental results are compared to the local relaxation processes of glassy polymers obtained by the already established measurement techniques such as dielectric relaxation and solid state NMR. Finally, the molecular interpretation of the relaxation of free-volume distribution in polymers will be discussed. 

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