TRIBOLOGICAL PROPERTIES OF ELECTROACTIVE POLYMERIC THIN-FILM BEARINGS

We report a preliminary study of the tribological properties of electroactive polymeric films. A total of 120 polymer films - either poly(pyrrole), poly(N-methylpyrrole), poly(5-carboxyindole) or poly(aniline) - were electrochemically deposited from an electrolyte solution containing the monomer onto a gold film that bad, in turn, been evaporated on to the convex face of polished glass substrates. These were rubbed against a fused-silica disc, of surface roughness 10 nm R(a), at a surface speed of 7.7 mm s-1. Theoretical and experimental analysis of thin film bearings shows that the frictional properties are strongly dependent upon the load, film thickness and bearing geometry, and therefore a constant applied normal force of 2 N is used throughout the experiments. Steady state and transient frictional forces were monitored by a sensitive pin-on-disc friction testing apparatus with a force resolution of 5 mN, which is described. Because the films were usually less than lO mum thick, the time required for the tribological characteristics of the substrate to dominate was used as a monitor of the wear of the films. It is shown that friction coefficients ranging from 0.70 to less than 0.02 can be achieved, and the value almost continuously controlled through choice of electrolyte solution and deposition parameters. It is also observed that the more durable materials generally showed higher frictional coefficients, which is characteristic of shear-related wear at the interface.