Study of the electric-field effect in polyethylene by the positron annihilation technique

The positronium formation and the reversibility behavior of the electric field from 31.75 to 588.24 kV/cm were studied in high-density polyethylene (HDPE) using the positron annihilation lifetime technique. The lifetime measurements were performed using the conventional fast-fast coincidence timing system. The observed ortho-positronium lifetime [tau][sub 3] does not show significant variation from the corresponding values measured without the electric field. On the other hand, the corresponding intensity I[sub 3] increases with increasing the electric field strength in the range from [approximately] 100 to 588.24 kV/cm. This result indicates a strong irreversible effect of the electric field. In addition, the effect of temperature on the sample stressed at 450 kV/cm was investigated. The structural changes on the heating and cooling cycles show reversible behavior. The thermal expansion coefficient has been deduced to be 7.53 [times] 10[sup [minus]3] C.