Atomic force microscopy, angle resolved x-ray photoelectron spectroscopy, and ellipsometry are applied to study the conformation of fluorocarbon polymers in molecularly thin liquid films, 5–130 Å thick, on solid surfaces. The combination of these techniques shows that the physisorbed polymers at the solid surface have an extended, flat conformation. In addition, the disjoining pressure of these liquid films is determined from atomic force microscopy measurements of the distance needed to break the liquid meniscus that forms between solid surface and force microscope tip. For a monolayer thickness of ∼7 Å, the disjoining pressure is ∼5 MPa, indicating strong attractive interaction between the polymer molecules and the solid surface. The disjoining pressure decreases with increasing film thickness in a manner consistent with a strong attractive van der Waals interaction between the liquid molecules and the solid surface.
Migration of very thin (<30 nm) polymeric films on solid surfaces was investigated quantitatively using two techniques—scanning microellipsometry and scanning small spot x-ray photoemission spectroscopy. The surface diffusion coefficient Ds increases as the film thickness decreases down to 1 nm, however, below 1 nm, Ds becomes independent of polymer film thickness. The functional dependence of Ds with molecular weight M is described, over the limited range of M in the unentangled regime, by M−1.7 The activation energy for polymer segment hopping is about 41 kJ/mol, which is similar to values obtained from bulk self-diffusion of other polymers.
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