Molecular aggregation structure and surface properties of poly(fluoroalkyl acrylate) thin films

The effects of side chain length on the molecular aggregation states and surface properties of poly(fluoroalkyl acrylate) [PFA-C-y, where y is the fluoromethylene number of the R-f groups] thin films were systematically investigated. Spin-coated PFA-C-y thin films were characterized by static and dynamic contact angle measurements, X-ray photoelectron spectroscopy (X-PS), differential scanning calorimetry, and wide-angle X-ray diffraction. The receding contact angles showed small values for PFA-C-y with short side chain (y <= 6) and increased for ones with y >= 8. It has been revealed that PFA-C-y with y >= 8 was crystallized and formed ordered structures. These results suggest that the water-repellent mechanism of PFA-C-y can be attributed to the presence of highly ordered fluoroalkyl chains at the outermost surfaces. The results of XPS in the dried and hydrated states and the contact angle measurement in water indicate that the contact angle for water is lowered by exposure of the carbonyl groups to the water interface through reorientation of short fluoroalkyl chains.