Dielectric spectroscopy secondary relaxation, processe

In Chapter 7, Mano and Dionisio describe how electrical methods, and particularly dielectric relaxation spectroscopy (DRS) and thermally stimulated depolarisation current (TSDS) techniques, play a major role as tools for e2q)loring molecular mobility. DRS enables molecular relaxational processes (both slow and fast) to be studied. For example, the localized motions of glass formers in the glassy state give rise to local fluctuations of the dipole vector that are the origin of the secondary relaxation processes detected by dielectric relaxation spectroscopy, while above, but near, the glass transition, cooperative motions result in a distinguishably different relaxation process (the a-relaxation). 

Broadband dielectric spectroscopy enables one to analyse the dynamics of polar groups in polymeric systems. Due to its broad frequency range of more than 10 decades a manifold of different molecular fluctuations can be studied from the dynamic glass transition (spanning already more than 10 decades in times) to secondary relaxations. Additionally one finds in chiral liquid crystals cooperative processes like soft-and Goldstone modes. 

The study of the aP coupling is advantageous in poly( -alkyl methacrylate)s due to the accessibility to the crossover region by both dielectric and mechanical spectroscopies and to the fact that both secondary and main processes are associated with high dielectric strength values, in contrast to a variety of other materials where the P relaxation is much less intense,. 

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