Surface structure and dynamics of block and graft copolymers having fluorinated poly(ethylene oxide) chain ends

The surface compositions of poly(styrene-b-ethylene oxide) and poly(styrene-g-ethylene oxide) films were found to be largely determined by the nature of the poly(ethylene oxide) (PEO) chain ends. Angle-dependent X-ray photoelectron spectroscopy revealed that polystyrene (PS) dominated the surfaces of the copolymers having PEO chain ends terminated by hydroxyl groups (SEO). Also, the PEO content decreased with decreasing sampling depth. In contrast, the surface regions of the corresponding copolymers having fluorinated PEO chain ends (fSEO) were dominated by PEO, and the PEO content increased with decreasing sampling depth. The fluorine content of fSEO also increased with decreasing sampling depth, indicating that the fluorinated chain ends were segregated at the outermost surface. The studied fSEO block copolymer seemed to have a higher surface concentration of fluorinated chain ends than the fSEO graft copolymers. Although it is likely that the fSEO surfaces were fully covered by fluorinated chain ends, the advancing water contact angles on fSEO films were markedly lower than on the corresponding SEO films. Moreover, low contact angles were retained even after prolonged annealing of the fSEO films in a vacuum. The surface behavior of BEO may be explained by the presence of flexible, fluorinated PEO chain ends, providing a highly dynamic surface. When fSEO films are immersed in water, the surfaces can rapidly restructure and expose PEO.