Spreading profiles of molecularly thin perfluoropolyether films

Perfluoropolyethers (PFPEs) are widely used as lubricants on magnetic recor ding media. The mobility of the PFPE on the protective carbon overcoat of t he media is widely accepted to be intimately coupled to the resulting tribo logical performance. The flow properties of molecularly thin films of nonpo lar PFPE Z and polar PFPE Zdol functions on solid surfaces were investigate d by measuring the spreading profiles. The spreading of Zdol exhibits terra ced profiles with the formation of a molecular foot, a shoulder and a verti cal step. To describe these features of Zdol spreading, we measured the Zdo l thickness dependence of the surface energy, which is then used to calcula te the thickness dependence of the disjoining pressure. The polar component of the Zdol surface energy exhibits oscillations as a function of PFPE thi ckness. The resulting oscillations in the disjoining pressure can be used t o qualitatively describe the origins of terraced spreading. The characteris tic Zdol spreading profile and surface energy oscillations of Zdol ave attr ibuted to molecular layering induced by polar interactions between the Zdol end-groups and the surface.