Surface modification of polyimide using dielectric barrier discharge treatment

We report on a novel method for the surface modification of polymers by direct exposure to a dielectric barrier discharge (DBD) at atmospheric pressure and room temperature. The polymer under treatment is located directly on the grounded electrode and serves at the same time as the discharge barrier. So far DBD treatment of the unfilled and Al2O3-filled commercially available polyimide foils have been investigated as a function of specific discharge energy. The morphological effects of the DBD treatment have been analysed by optical microscopy, SEM, AFM, and chromatic coding distance measurement while XPS was used for analysis of the chemical surface composition. The results can be summarised as follows: Firstly, the etching rate of the polyimide (PI) surface by DBD in air is rather high leading to a pronounced roughening within some tens of seconds. Secondly, the attack is dependent on whether the polyimide contains a filler, which is added to improve the thermal conductivity of the material. In this case the etching lays bare the grains of the filler but is spatially rather uniform. The surface roughening increases the bond strength to coating layers. Finally, in the unfilled material crater-like structures are observed which are attributed to the repetitive ignition of discharge filaments in the same location.