Some unexplained disturbing phenomena in the electrical properties of dielectric polymers

In this paper, we address some poorly explained problems associated with electrical properties of dielectric polymers. Charge injection is often unclear due to metal-polymer interfaces phenomena including poor contacts, asperities and electrochemical reactions. We also review some difficulties involving the sample bulk, the most important being the influence of the sample size on aging and breakdown. We show many results obtained with a wide variety of (reasonably pure and defect-free) polymers suggesting that in addition to thickness, the electrodes area is also a parameter. The negative resistance often observed in conductivity measurements is also discussed. The fact that C-C bonds are more easily broken than expected implies that this phenomenon must be looked at more carefully. The role of the free radicals thus created requires more attention. It is suggested that the interpretation of several measurements, mobility for example, might require some revision. Among other things, interpreting results using only an activation energy is not likely to give a correct description of the measured phenomenon since entropie effects are quite significant with most polymers. Finally, one may wonder if the usual explanation for some trapped sites in the so-called forbidden band of polyethylene still makes sense considering the fact that charge transport is mainly affected by the bonds broken by the applied stress.