Influence of electric field and pressure on conduction of polyethylene

We have shown that the compensation law observed in PE between ∼0 and 80°C is due to the linear relation between the activation enthalpy and entropy. Both variables are proportionnal to the volume of activation(as long as it remains small) and which is varying under the influence of pressure and field. ΔH and ΔS are also related to the thermal expansion and compressibility coefficients and to a constant itself related to the Grüneisen constant. The ionic field due to water has been estimated to be ∼1.85 × 10
⁷
Vm
⁻¹
and it can dominate electrical measurements at low fields. This demonstrates that it is impossible to obtain reproducible or comparable results if the experimental conditions are not completely identical and the desirability of doing measurements under a very good vacuum. One definitive conclusion is that the decrease of ΔH and ΔS under large applied stresses modify considerably the intrinsic properties of the polymer.