Morphology of poly(methyl methacrylate) and polystyrene blends upon Langmuir-Schaefer deposition

Langmuir-Schaefer (LS) deposition of poly(methyl methacrylate) (PMMA) and polystyrene (PS) 10 : 1 and 5 : 1 (mass ratios) blends has been investigated by recording (i) surface pressure isotherms of the Langmuir films at the air/water interface and (ii) atomic force microscopy (AFM) images of the LS films deposited on silica substrates. The results suggest a complete phase separation of PMMA and PS at the air/water interface resulting in a PMMA monolayer on top of which PS islands anchor. However, upon LS dipping, the transfer of PMMA onto the solid substrate is obstructed by the PS domains, which leads to a morphology where a continuous PMMA layer is located at the air-exposed surface. The resulting LS film is thus not a stamped replica of the corresponding floating Langmuir film. The results of this study give new insights for the preparation of bicomponent LS films, especially those containing blends of immiscible polymers.