Electrical conduction on the surface of aged polymer

Reports some results of an investigation of surface conductivity of untreated and γ-irradiated polyethylene at relative humidity in the range of 0-80%. A commercial grade of LDPE of 40 μm thickness has been used in this work. The film surfaces were initially cleaned with isopropyl alcohol in an ultrasonic bath before an interdigital electrode (aluminium) system was vacuum (10^-5 torr) deposited on one surface of the film. Each element of the electrode system was 2 mm wide and 30 mm long and separated from its adjacent member by 2 mm, the electrode thickness being 0.1 μm in each case. The interdigital electrode system allows a relatively large interaction path without the need for very large samples. The electroded sample was then located with its electrodes shorted, on a PTFE sample holder in a stainless steel measurement chamber which was subsequently evacuated to a pressure of 0.01 torr. The sample was maintained in this condition for at least sixteen hours at a constant temperature of 25°C. At the end of the sixteen hour period of sample conditioning a step voltage of the desired magnitude was applied to one set of interdigital electrodes while the other set was connected to earth through an electrometer