Electric space charge threshold observation in polyurethane under high electric fields

Polyurethanes have been extensively studied for their strong electromechanical response. Previous studies have mainly investigated the impact of electrical charges on these polymers' DC conductivity, which was measured on the order of 10−10 S/m. The movement of electric charges is responsible for the macroscopic deformation of polymer films under an electric field. However, this study focused primarily on electric fields below 107 V/m, where the electric current complies with Ohm's law. In this paper, we examine the electric current above this field value and observe a deviation in the current from linearity with the applied field, especially for a high electric field of 106–107 V/m. This change is known in polymers under high electric fields but has never been observed in polyurethane. This suggests the injection of electrode charges into the polymer material. This article provides the threshold at which the transition occurs from linear (Ohm's law) to nonlinear conduction as a result of injected electric charges.