Miscibility induced by confinement in mixed monolayer films

Both poly(methyl methacrylate) (PMMA) and poly(ethylene oxide) are known to be immiscible with poly(styrene). PMMA is found to be miscible with poly(ethylene oxide). Therefore, PMMA is predicted by the mean field theory to be immiscible with poly(styrene-b-ethylene oxide) (PS-b-PEO) in the bulk state. The miscibility of PMMA with PS-b-PEO may be different in the two-dimensional state. The mixed monolayer behavior of stereoregular (including isotactic, atactic and syndiotactic) PMMA and PS-b-PEO was investigated in this article on the basis of the measurements of surface pressure–area per molecule (π–A) isotherms at three different temperatures. The miscibility and nonideality of the mixed monolayers were examined by calculating the excess area as a function of composition. Mostly negative deviations from ideality were observed in the mixed monolayers at 25 °C and 32.5 °C. This is likely because of favorable interaction between PMMA and PEO. However, positive deviations occurred at 32.5 °C and 40 °C with atactic PMMA (or syndiotactic PMMA) mixed monolayers. With confinement in the two-dimensional state, the miscibility between PMMA and PS-b-PEO was greatly improved in comparison with the bulk state.