Effects of the CNT Network Size and Interphase on Mode I Fracture of Buckypaper Nanocomposites

Buckypaper (BP) is a complex 3D CNT structure with randomly distributed CNTs. The size of the CNT network and interphase can potentially affect the fracture behavior of BP nanocomposite on a larger length scale. For multiwall carbon nanotube BP, the main pore sizes range between 20–35 nm (intrabundle) and 65–110 nm (inter bundle). Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) have proven nano and sub-micron inhomogeneities in BP membranes. These inhomogeneities affect the macroscale mechanical response of BP membranes due to the local high modulus mismatch among CNT particles, the CNT networks, and the polymer. The geometry (shape and size) and the spatial locations (depth and distance between the networks) of the buried CNT networks are amongst critical parameters for the degree of the mechanical mismatch. Atomic Force Microscopy-based Peak Force Quantitative Nanomechanics Mapping (PFQNM) technique is used to quantify the nano- and micro-properties of CNT networks and interphase. Double Cantilever Beam (DCB) specimens are used for mode I fracture characterization. The compliance Calibration technique is used to calculate the initiation and propagation energy release rate. The authors use the Weibull model to examine material properties’ statistical distribution. Weibull statistics link the probability of an event such as CNT network size and interphase thickness.