Maxwell–Wagner–Sillars polarization

In dielectric spectroscopy, large frequency dependent contributions to the dielectric response, especially at low frequencies, may come from build-ups of charge.

This, so-called Maxwell–Wagner–Sillars polarization (or often just Maxwell-Wagner polarization), occurs either at inner dielectric boundary layers on a mesoscopic scale, or at the external electrode-sample interface on a macroscopic scale. In both cases this leads to a separation of charges (such as through a depletion layer). The charges are often separated over a considerable distance (relative to the atomic and molecular sizes), and the contribution to dielectric loss can therefore be orders of magnitude larger than the dielectric response due to molecular fluctuations.

Maxwell-Wagner polarization processes should be taken into account during the investigation of inhomogeneous materials like suspensions or colloids, biological materials, phase separated polymers, blends, and crystalline or liquid crystalline polymers.

The simplest model for describing an inhomogeneous structure is a double layer arrangement, where each layer is characterized by its permittivity ${\displaystyle \epsilon '_{1},\epsilon '_{2}}$ and its conductivity ${\displaystyle \sigma _{1},\sigma _{2}}$. The relaxation time is then: ${\displaystyle \tau _{MW}=\epsilon _{0}{\frac {\epsilon _{1}+\epsilon _{2}}{\sigma _{1}+\sigma _{2}}}}$ Importantly this shows that an inhomogeneous material may have frequency dependent response, even though none of the individual inhomogeneities severally are frequency dependent.

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