Multitechnique surface analysis of poly(N-vinylpyridine-co-styrene) and poly(N-vinylimidazole-co-styrene) random copolymers

The surface structure and bulk compositions of random copolymer systems based on poly(N-vinylpyridine) (N = 2, 4) and poly(N-vinylimidazole) copolymerized with polystyrene were examined by X-ray photoelectron spectroscopy (X.p.s.) or electron spectroscopy for chemical analysis, Fourier transform infra-red spectroscopy (FTi.r.) and static secondary ion mass spectrometry (s.i.m.s.). The spectroscopic results were correlated with morphology determined from scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The X.p.s. results from solution-cast thick films and films cast at the air/water interface from poly(N-vinylpyridine-co-styrene) copolymers indicate equivalent surface and bulk compositions for all angle- and energy-dependent measurements, which are further supported by FTi.r. and EM analyses. On the other hand, surface enrichment of polystyrene was observed in angle-dependent X.p.s. analysis of poly(N-vinylimidazole-co-styrene) preparations. Attenuated total reflectance and transmission i.r. peak intensity ratios are equivalent, which suggests that segregation of polystyrene in the poly(N-vinylimidazole-co-styrene) system is localized to a region less than 30 Å from the air/polymer interface. In addition, the s.i.m.s. technique was shown to be sensitive to structural differences arising from pH changes as well as to the detection of dimer ions in these systems.