Dielectric relaxation overall permittivity

In Section 4, we have examined, from a fundamental point of view, how temperature and cure affect the dielectric properties of thermosetting resins. The principal conclusions of that study were (1) that conductivity (or its reciprocal, resistivity) is perhaps the most useful overall probe of cure state, (2) that dipolar relaxations are associated with the glass transition (i.e., with vitrification), (3) that correlations between viscosity and both resistivity and dipole relaxation time are expected early in cure, but will disappear as gelation is approached, and (4) that the relaxed permittivity follows chemical changes during cure but is cumbersome to use quantitatively. 

Dielectric spectroscopy is concerned with the dependence of complex permittivity on temperature and frequency. The relatively low level of d.c. conduction in polycarbonate ensures that the principal relaxations associated with polycarbonate s active C 0 dipole can be observed over a useful range of frequency and temperature. In multi-phase or multi-component polymers charge accumulation at the sub-structure interfaces leads to Maxwell-Wagner-Sillars (MWS) contributions to the overall polarization. 

Dielectric spectroscopy is a very promising tool to probe relaxation processes, especially since new broadband equipment can cover frequencies in the range of lO"" to 10 ° Hz. The theoretical introduction of this technique can be found in literature (Korhonen et al. 2008). Basically, electrodes of two different sizes are used, and the overall response, given by capacitance (C), depends on both the intrinsic characteristics (permittivity e) and the geometry of the sample. The relationship between capacitance and sample geometry is given by ... 

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