The effect of substrate on the phase morphologies of PMMA/PS blend films was investigated by means of phase contrast microscope. PMMA/PS blend films were cast onto various substrates(such as glass substrate and PP substrate) by spin-coating with thickness of about 10 μm. It was observed that there was a large difference of the phase inversion region between the blend films cast on glass and on PP substrates. On glass substrate, the phase inversion occurred at about \%Φ\%_m=0 4(PS mass fraction) while at \%Φ\%_m=0 5 on PP substrate. This implies that there is a shift of the phase inversion region with the change of substrate in cast polymer blend films. In other words, phase inversion region depends on the substrate. ATR-FTIR analysis was used to detect the composition of the surface and the bottom of the films(about 100 μm thick) obtained by evaporating solvent from the polymer blend solution. The ATR-FTIR spectra of the surface and the bottom of the PMMA/PS blend thin films cast on glass substrate and PP substrate showed that PMMA component preferentially segregated to glass substrate and PS component was enriched on the PP substrate. This selective segregation was due to the difference of the wetting abilities of PS and PMMA on the two kinds of substrates. The polymer-substrate interfacial tension γ were calculated and the results supported the ATR-FTIR results. It could be inferred that the shift of the phase inversion region with the change of the substrate in PMMA/PS blend film was due to the fact that the composition of the blend in the bulk changed, owing to the selective enrichment of one component of polymer blend to the substrate. In other words, the affinity between polymer and substrate can strongly influence the phase morphologies and the phase inversion region in polymer blend films.
