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

We present measurements of the nanoscale elastic and viscoelastic propertie s of samples of poly(methylmetacrylate) (PMMA)/rubber nanocomposites. For t hese studies we have used a new technique based on atomic force microscopy (AFM) with ultrasonic excitation, heterodyne force microscopy (HFM), which provides a means of testing the viscoelastic response of polymeric material s locally (in tip-probed regions) at MHz frequencies. Phase-HFM contrast di stinguishes local differences in the dynamic response of PMMA/rubber compos ites. Comparison of HFM with other AFM-based techniques (ultrasonic force m icroscopy, friction force microscopy and force modulation microscopy), whil e imaging the same surface region, emphasizes the unique capabilities of HF M for these kinds of studies, and reveals key nanostructural characteristic s of the composites. Some of the toughening particles appear to be broken d own, with areas of PMMA detached from the surrounding matrix.