The electrical behaviour of an insulating liquid layer between polymer sheets under A.C. voltage

The diffuse part of the electric double layer spontaneously present at an insulator/liquid interface can be displaced by an A.C. field. It is shown that the diffuse part of the double layer acts as a reservoir of ions which gives rise to a time-limited unipolar injection. At low fields, tanδ increases when the voltage V is increased. At high fields, the reservoir of charges depletes quickly and the charges swept away by the field are stopped by the opposite wall, tanδ then decreases in a similar way to the Garton effect, although the physical model is completely different. Experimental results are in agreement with the theoretical predictions. The influence of liquid conductivity, space charge and electrohydrodynamic liquid motion is discussed.