THE EFFECT OF INTERFACIAL POTENTIAL ON FRICTION IN A MODEL AQUEOUS LUBRICANT

A tilting electrochemical cell was used to study the effect of potential on the static coefficient of friction of iron on mild steel in a model aqueous lubricant consisting of octanoic acid neutralized to pH 9.2 with sodium hydroxide. A sharp fall in friction was observed at potentials positive of -400 mV vs. standard hydrogen electrode. Both impedance and radiotracer measurements indicated that the decrease in friction coincided with an increase in the thickness of a lubricating surface film. This potential dependent behavior is interpreted in terms of electrostatic interactions between the iron and the negatively charged octanoate species.