The relationship between PFPE molecular rheology and tribology

Abstract

The tribology of several perfluoropolyether (PFPE) lubricants was studied using a pin on disk (POD) test. During the POD test, PFPE is incrementally removed from the track with each sliding cycle. The number cycles to failure, NF, is detected as a sudden increase in the friction coefficient. Molecular theory for polymer melt rheology was employed to develop a universal scaling rule. The PFPE removal rate coefficient is proportional to a parameter containing the bulk viscosity, degree of polymerization, and temperature and structure scaling coefficients. The parameter is a measure of the frictional resistance to segmental sliding along the surface in the contact zone. The temperature scaling coefficient corrects for the absence of free volume in the molecularly-thin lubricant film. The structure scaling coefficient accounts for differences in the energy barriers to internal rotation. This is the first description of a relationship for the tribological properties of PFPEs that takes into account their viscosity, molecular structure, degree of polymerization, and temperature. © J.C. Baltzer AG, Science Publishers.