Complex terraced spreading of perfluoropolyalkylether films on carbon surfaces

Complex molecular layering of OH-terminated perfluoropolyalkylether films o ver amorphous carbon surfaces has been observed using spatially resolved mi croellipsometry. The first layer is diffusive in nature, and the subsequent layers exhibit sharp steps of about twice the thickness of the first layer . This behavior, characteristic of a coexisting two-dimensional gas, with c ohesive, liquidlike multilayers, is in clear contrast with that of the CF3- terminated analog, which shows a smooth diffusive profile. In this particul ar case, spreading, for thickness greater than one monolayer, can be exactl y described by a Poiseuille flow in a disjoining pressure gradient originat ing solely from van der Waals interactions. For both types of polymers, dif fusion rate reaches a maximum at full monolayer coverage, and decreases in the submonolayer regime. Spreading for both types of polymers unambiguously follows a t(1/2) time dependence. [S1063-651X(99)05601-9].