Amphiphilic block copolymer surface composition: Effects of spin coating versus spray coating

Spray coating is demonstrated to produce different surface compositions of block copolymer films than spin coating even after annealing above the glass transition temperatures of both blocks. An amphiphilic block copolymer derived by chemically modifying the polyisoprene block of a polystyrene-block-poly(ethylene-ran-butylene)-block-polyisoprene precursor with different molar ratios of 550 g/mol poly(ethylene glycol) monomethyl ether and a semifluorinated alcohol, 10-Perfluorodecyl-1-decanol, is used as a model system to investigate the effect. X-ray photoelectron spectroscopy demonstrated significantly higher amounts of CF2 and CF3 carbons at the surface for spray coated films while the overall concentration of C-O bonded carbons did not change. Near edge X-ray absorption fine structure spectroscopy shows a larger C1s -> sigma*(C-F) transition partial electron yield peak for the spray coated films and a negligible amount of polystyrene populating the surface for both solution deposition techniques. Water contact angles measured by the captive air bubble technique are found to be higher for the spray coated samples upon immersion in water. Scanning force microscopy also shows significant differences in the surface morphology of both films. These results indicate that it should not be assumed that the surface composition of a spin coated polymer film is representative of the same polymer deposited by spray coating. (C) 2012 Published by Elsevier Ltd.