Effect of Surface Cleaning on Performance of Organic Friction Modifiers

The performance of surface-active additives, such as friction modifiers, depends on their interactions with surfaces. Their effectiveness thus hinges upon the surface conditions. In this work, the effect of cleaning methods of test substrates on the friction reduction capabilities of different organic friction modifier (OFM) additives was investigated. 52100 steel discs and balls were the test specimens. They were cleaned in five different ways. The cleaned surfaces were characterized by using ellipsometry and atomic force microscopy. The tribological performance of stearic acid (STA), octadecylamine (ODA), and octadecanol (ODO), on these surfaces was then tested.

As-received steel surfaces were covered with contaminants that may impede the formation of an OFM surface layer. Cleaning these surfaces with solvents cannot completely remove these contaminants. Cleaning with oxygen or argon plasma results in cleaner surfaces compared to those cleaned by solvents only. The impact of the choice of cleaning method on friction depends on the strength of the interaction between the OFM and the steel surface, which determines the ability of an OFM to displace surface contaminations. Cleaner surfaces result in lower initial friction for STA and ODA. Steady-state friction is also affected but to a lesser extent. This may be because most contaminants that remained in the wear track were mechanically removed during rubbing.