Heterodyne force microscopy of PMMA/rubber nanocomposites: nanomapping of viscoelastic response at ultrasonic frequencies

Abstract

We present measurements of the nanoscale elastic andviscoelastic properties of samples of poly(methylmetacrylate)(PMMA)/rubber nanocomposites. For these studies we have used a newtechnique based on atomic force microscopy (AFM) with ultrasonicexcitation, heterodyne force microscopy (HFM), which provides a means oftesting the viscoelastic response of polymeric materials locally (intip-probed regions) at MHz frequencies. Phase-HFM contrast distinguisheslocal differences in the dynamic response of PMMA/rubber composites.Comparison of HFM with other AFM-based techniques (ultrasonic forcemicroscopy, friction force microscopy and force modulation microscopy),while imaging the same surface region, emphasizes the unique capabilitiesof HFM for these kinds of studies, and reveals key nanostructuralcharacteristics of the composites. Some of the toughening particles appearto be broken down, with areas of PMMA detached from the surroundingmatrix.