Diblock copolymer ultrathin films studied by high resolution electron energy loss spectroscopy

Surface segregation of polymers forming thin films is relevant in several industrial applications. This paper studies the influence of preparation parameters on the surface composition of poly(ethylene oxide)–polystyrene diblock copolymer ultrathin films. Silicon wafers were used as substrates. The film preparation method (spin coating vs. casting followed by solvent evaporation), solvent (THF vs. CCl4), annealing vs. non-annealing and the substrate nature (native silicon oxide vs. silanized substrate) were analyzed. High resolution electron energy spectroscopy in vibrational energy loss range was used to estimate the extreme surface composition. Generally, THF favors the surface segregation of polystyrene. After annealing, whatever the preparation method, the polystyrene preferentially segregates at the surface without forming a pure overlayer. These results were compared with the surface compositions calculated from X-ray photoelectron spectroscopy spectra of the films.