AFM and UFM surface characterization of rubber-toughened poly(methyl methacrylate) samples

The microstructure of a series of injection-molded and extruded rubber-toughened poly(methyl methacrylate) (RTPMMA) samples was investigated. Atomic force microscopy (AFM) and ultrasonic force microscopy (UFM) were used to study surface topography and local elastic properties. AFM topography measurements combined with UFM can reveal the distribution and orientation of the rubber particles in the PMMA matrix. UFM, in particular, reveals the core-shell structure of the particles as well as the presence of particles immediately under the surface, otherwise invisible, In some cases the particles appear to be covered by a thin PMMA layer, whereas in other cases they appear to have broken, thereby exposing parts of their internal structure. Generally, the particles are elongated in the skin region of the injection-molded samples. On the other hand, the particles in the surface region of the extruded samples appear to be almost spherical. The observed difference is attributed to the fountain flow phenomenon, which takes place during injection molding. (C) 2001 John Wiley & Sons, Inc.