THE BEHAVIOR OF POLYMER-SOLUTIONS IN CONCENTRATED CONTACTS - IMMOBILE SURFACE-LAYER FORMATION

The film-forming properties of solutions of low-to-medium molecular weight polyisoprenes in synthetic hydrocarbon have been studied using thin film interferometry. It has been shown that the lubricating films formed in rolling, concentrated contacts have two components. At very slow speeds, the polymer forms an immobile film of thickness equivalent to two radii of gyration of the polymer molecules. This film thickness is independent of speed but is gradually squeezed from the contact when motion is halted. The film is likely to represent two monolayers of polymer, one on each surface, and can be regarded as a boundary lubricating film. As the rolling speed is raised, a conventional elastohydrodynamic film is formed which is superimposed on the immobile film. The immobile films formed are similar to those detected using a force balance apparatus and reported elsewhere in the literature.