Novel Interfacial Adhesion Experiments with Individual Carbon Nanofibers

A novel experimental method for the interfacial mechanics of nanofibers embedded in polymeric matrices was developed. The debond force was determined by MEMS devices whose motion was precisely measured from optical images by digital image correlation. This method is based on a novel approach to embed nanofiber and nanotubes in a thermoplastic or thermosetting polymer with submicron control of the embedded length and orientation of the nanofiber. The cross-head displacement resolution of this optical method is ~20 nm and the force resolution is of the order of nanonewtons. A traceable force calibration technique was integrated to calibrate the MEMS force sensors. Experiments were conducted for the first time with vapor grown carbon nanofibers embedded in EPON epoxy to reveal the role of nanofiber surface roughness and functionalization in the interfacial shear strength. It was established that the nanoscale surface roughness of nanofibers strongly promotes interfacial strength while surface functionalization can increase the interfacial adhesion strength by more than a factor of three. The present experiments are the first of their kind both in their fidelity and accuracy of the applied experimental method and the data scatter is dramatically reduced compared to prior experimental attempts.