Nanomechanical mapping of composite interphases with contact resonance AFM
D.C. Hurley, S.S. Nair, S. Wang
National Institute of Standards & Technology, US
Keywords: AFM, nanomechanics, modulus, composites
Abstract:The superb spatial resolution and imaging capability of atomic force microscopy (AFM) are attractive for materials characterization in many nanotechnology applications. However, AFM-based approaches often cannot provide quantitative data for detailed modeling. Contact resonance AFM (CR-FM) promises quantitative imaging (mapping) of nanoscale mechanical properties. In CR-FM, the resonant frequencies of cantilever vibrations while the tip is in contact provide information about nanomechanical properties such as elastic modulus. For CR-FM imaging, we have developed custom electronics that interface with a commercial AFM. In one application, we used CR-FM to characterize the interphase of a fiber-reinforced composite. The mechanical properties of this nanoscale region, for instance modulus and stress transfer, are critical to the composite’s macroscale structural performance. Yet most techniques lack sufficient spatial resolution to directly characterize the interphase. We performed CR-FM experiments on a composite containing cellulose microfibers in a polypropylene matrix. Modulus maps with a spatial resolution of approximately 10 to 16 nm were obtained. The maps showed a transition region between the fiber and the matrix with an average width of 70 nm. Results on other samples showed differences in the average interphase width depending on the processing chemistry.