Characterization of the interphase in carbon fiber/polymer composites using a nanoscale dynamic mechanical imaging technique

The interphase of fiber reinforced polymer composites is a narrow region around the fiber, and the mechanical performance of a composite strongly depends on the properties of the interphase. The interphase of carbon fiber reinforced polymer composites (CFRPs) is difficult to quantitatively characterize because of its nanometer dimension. To solve this problem, we present a nanomechanical imaging technique for mapping the dynamic mechanical property around the interphase region in CFRPs, and for providing nanoscale information of the interfacial dimension. The experimental results show that this method can determine the width and topography of the interphase with nanoscale lateral resolution, based on the storage modulus profile on the cross section of the composite. The average interphase thicknesses of a T300 carbon fiber/epoxy resin composite and a T700 carbon fiber/bismaleimide resin composite are 118 nm and 163 nm, respectively, and the size of interphase is uneven in width and "river-like", which is consistent with the surface topography of the carbon fibers. Furthermore, the effect of water-aging on the interphase of the T300/epoxy composite was analyzed using the in situ imaging technique. An increase in the interphase width and interface debonding were revealed, implying a degradation in the interphase region.