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

Effects of side chain length on the molecular aggregation states and surface properties of poly (fluoroalkyl acrylate)s [PFA-C-y, where y is the fluoromethylene number in R-f group] thin films were systematically investigated. Spin-coated PFA-Cy thin films were characterized by static and dynamic contact angle measurements, X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry and wide-angle X-ray diffraction. The receding contact angles showed small values for PFA-Cy with short side chain (y <= 6) and increased above y >= 8. Results revealed that the fluoroalkyl side chain of PFA-Cy with y >= 8 was crystallized and formed ordered structures. These results suggest that the water-repellent mechanism of PFA-Cy can be attributed to the presence of highly ordered fluoroalkyl side chains at the outermost surfaces. The results of XPS in the dry and hydrated states and contact angle measurement in water support the mechanism of lowering contact angle for water by exposure of carbonyl group to the water interface through reorientation of short fluoroalkyl chains. The surface nanotexture was formed on PFA-C-8 through imprinting of anodic aluminum oxide films with a pore diameter of 200 nm. This nano-imprinted surface showed extremely high hydrophobicity as well as high oleophobicity.