The miscibility and phase separation of poly(methyl methacrylate) (PMMA) and styrene-acrylonitrile (SAN) have already been investigated using various methods. However, these methods have limitations that often result in inconsistent characterization. Consequently, the reasons for the dependence of miscibility on composition as well as on processing temperature have not yet been proved. The phase separation of PMMA/SAN blends was therefore investigated for the first time using a novel technique, nanoscale AFM-IR. It couples nanoscale atomic force microscopy (AFM) with infrared (IR) spectroscopy. Therefore, the phase morphology can be chemically identified and precisely classified within the nm-regime. The PMMA/SAN blends, on the other hand, were analyzed of their changes in morphology under different thermal treatments. It was possible to visualize and define the phase separation, as well as dependence of the miscibility on the mixing ratio. In the miscible domain, no two individual phases could be detected down to the nanometer range. It was shown that with increasing temperature, the morphology changes and two different phases are formed, where the phase boundaries can be sharply defined. The onset of these changes could be identified at temperatures of about 100 °C.
Keywords: PMMA/SAN blends; miscibility; nanoscale AFM-IR; phase separation.