Comparison between AFM-based methods for assesing local surface mechanical properties of PDMS-silica composite layers
(English)Manuscript (preprint) (Other academic)
Local surface mechanical properties of polymeric nanocomposites play a significant role in theirperformance. Atomic Force Microscopy (AFM) can be used to perform measurements of suchproperties with high lateral resolution. The interphase between filler and matrix, and how it can becontrolled by means of surface chemistry is of particular interest. In this work we compare threeoperating modes of AFM: Tapping mode, PeakForce QNM (Quantitative Nanomechanical Mapping)and Intermodulation AFM (ImAFM), for their ability to capture the tip-surface force and to extractlocal mechanical properties by applying different contact mechanics models. Layers ofpoly(dimethylsiloxane) (PDMS) with and without 20 wt.% of hydrophobic silica nanoparticles werestudied employing these AFM modes. We show that tapping mode AFM can provide qualitativeinformation, but it is insufficient to accurately and quantitatively discriminate surface propertiessince this mode does not allow extraction of the tip-surface force. Quantitative mapping ofmechanical properties is possible with both PeakForce QNM and ImAFM. However, it remained achallenge to evaluate the data for soft PDMS layers with PeakForce QNM. Local surface mechanicalproperties could be more reproducibly assessed via ImAFM. We show that the Tapping modeimages for pure PDMS report a relatively homogeneous surface, but as we utilize PeakForce QNMand ImAFM more details appear and the inhomogeneous nature of the surface layer becomesapparent. Incorporation of silica particles in the PDMS layer results in a significant increase in theapparent stiffness of the matrix. All imaging modes allow visualization of the hard particles in thesoft matrix. However, we were most successful with imaging the interphase using ImAFM.
Nanomechanical properties, nanocomposites, Atomic Force Microscopy, Scanning probe microscopy, intermodulation, PDMS, elastic modulus, viscoelasticity
Engineering and Technology
IdentifiersURN: urn:nbn:se:kth:diva-175404OAI: oai:DiVA.org:kth-175404DiVA: diva2:860824
QS 20152015-10-142015-10-142016-02-11Bibliographically approved