In this paper, we investigate the surface properties of a series of copolymers of perfluoroalkyl methacrylate (CH2 = C(CH3)COOCH2CnF(2n + 1), n = 1, 6, or 10) and methyl methacrylate (MMA) and of blends of perfluorooctyl-end-capped poly(methyl methacrylate) (PMMA) and pure PMMA. The introduction of perfluoroalkyl groups significantly lowers the polymer surface energy as determined by the acid-base approach. X-ray photoelectron spectroscopy (XPS) confirms a higher fluorine concentration in the surface region (the outer 3.8 nm) as compared to in the bulk. The fluorine density in the outermost atomic layer is quantitatively determined by low-energy ion scattering (LEIS). A linear relationship is found between the fluorine density in the outermost atomic layer and the surface energy of the partially fluorinated polymethacrylates, irrespective of the length of the perfluoroalkyl chain. This linearity confirms Langmuir's "principle of independent surface action". Deviation from this linear relationship exists for both highly and sparsely fluorinated polymethacrylates and can be ascribed to the local (surface) ordering of the fluorinated tails and MMA units, respectively. This study may offer one further step toward a deeper understanding of the correlations between macroscopic surface properties and microscopic surface chemical composition.

The outermost atomic layer of perfluorinated thiol monolayers on gold and poly(tetrafluoroethylene) (PTFE) is analyzed by low-energy ion scattering. Absolute quantification of fluorine density in this layer was achieved after calibrating the fluorine signal with a freshly cleaved LiF(100) single crystal. The fluorine density of monolayers of a C8F17-thiol on gold was 1.48 x 10(15) F atoms/cm2, whereas for PTFE a value of 1.24 x 1015 F atoms/cm2 was observed. This difference was explained by the different tilt angles of the thiol on gold and PTFE chains with respect to the surface normal. Both a configurational and a molecular interpretation on the perfluorinated thiol monolayer on gold are given.

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The present revolution in novel organic materials is driven by the synthesis of new materials exhibiting specific functional properties. Traces of silicon compounds are often present in these materials and, although the bulk concentrations of these impurities may be low, segregation can seriously modify the surface composition. Surfaces and interfaces play an important role in many applications, and the intrinsic properties of the materials are thus often obscured by the presence of segregated impurities.By studying silicon impurity segregation in poly-dialkoxy phenylenevinylene (PPV), polycarbonate and dendrimer macromolecules, we demonstrate how low-energy ion scattering may be used to determine the surface impurity fraction and to observe which groups at the surface are shielded by the segregated species. We demonstrate that the performance of PPV-based light-emitting diodes is significantly reduced for submonolayer coverages of siloxanes. We find that the kinetics of the segregation process depend strongly on the materials and the sample preparation conditions. We find that the presence of solvents is needed to enable segregation at room temperature. Heating does enable siloxane impurity segregation in polycarbonate in the solid phase, whereas for polydimethylsiloxane in PPV films we find that segregation in the solid phase does not occur up to 200• C. The siloxane molecules are found to segregate to preferential sites at the surface, shielding the polar groups. Finally, we demonstrate that purification of the surface is often possible through simple procedures that provide an easy way to study the intrinsic properties of the materials.

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