Surface chemical composition analysis in polystyrene/poly(vinyl methyl ether) blend films by UV reflection spectroscopy

Surface chemical composition in miscible polymer blend films was measured by UV reflection spectroscopy, using polystyrene (PS) as chromophores in blends with poly(vinyl methyl ether) (PVME). Kramers-Kronig transformation from UV reflection spectra was performed to obtain the optical constant (k) spectra, from which the surface composition of PS in blend films was estimated. The results show surface excess of PVME in a range of bulk blend compositions when M-w of PS and PVME was 240 000 and 99 000, respectively. This surface composition probes the surface depth of several hundreds of angstroms, which is deeper than the probed depth of ESCA but shallower than that of IR-ATR. In miscible PS/PVME blends, the experimentally obtained surface composition facing air compares well with the prediction from the simplified mean-field theory of Jones and Kramer but shows less PVME enrichment than the results by ESCA. For the in-situ technique, UV reflection via bifurcated fiber-optic accessory was found to provide similar results as the reflection accessory. Also, the polymer-quartz interface and heat treatment effects were investigated. The polymer-quartz interface showed less enrichment of PVME than the air-facing surface, while the blend surface facing air was more enriched in PVME after thermal treatment.