Dielectric relaxation spectroscopy principles

The rates of change (slopes of the curves) of many important properties (such as the refractive index, surface tension, and gas permeabilities) as a function of temperature, the value of the dielectric constant, and many other optical and electrical properties, often change considerably at Tg. These changes enable the measurement of Tg by using techniques such as refractometry and dielectric relaxation spectroscopy. Refractometry provides results which are similar to those obtained from dilatometry, because of the correlation between the rates of change of the specific volume and of the refractive index with temperature. Dielectric relaxation spectroscopy is based on general physical principles which are similar to those in dynamic mechanical spectroscopy, the main difference being in its use of an electrical rather than a mechanical stimulus. 

Dielectric relaxation spectroscopy can probe the very broad time domain between 10 and 10 s. In principle, therefore, this method can be used... 

In conclusion, although DMTA and dielectric spectroscopy involve very different stimuli, the information they provide is complementary and similar basic principles apply to both. Consequently, the pair can be used in tandem to provide a more comprehensive picture of the molecular relaxation processes that occur within polymeric materials. 

Schreyer et al. [881] have reviewed the theoretical principles of dielectric behaviour (e.g. polarisation, relaxation, relaxation time and spectrum, frequency and temperature variation, activation energy) several books are also available [878-880]. Monographs on dielectric spectroscopy of polymeric materials have appeared [877,882]. 

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