Field-induced Changes in the Viscoelasticity of Polyethylene

Using an acoustic shear wave resonator operating at ~5 MHz frequency, measurements of the shear moduli of low density polyethylene films under steady applied fields up to 1.8 kV/mm have been made. Both the storage and loss moduli are found to be functions of the field, the onset of change correlating with the onset of increased current in the films. It is suggested that the shear waves interact with short segments of the polyethylene chains which undergo conformational relaxations in the same frequency range. The measurements support a model in which the electric field directly increases strain in the amorphous phase of the polymer, a condition conducive to void formation as a prelude to breakdownn.