Quantifying the interfacial load transfer in electrospun carbon nanotube polymer nanocomposite microfibers by using in situ Raman micromechanical characterization techniques

The interfacial load transfer is of paramount importance to the bulk mechanical properties enhancement in nanotube-reinforced nanocomposites. Recent single-nanotube nanomechanical pull-out studies report quantitative interfacial load transfer characteristics of nanotube-matrix interfaces in close-to-ideal interfacial binding configurations. However, the elucidation of the actual interfacial load transfer in bulk nanotube nanocomposites remains a significant challenge due to the presence of many complex and inevitable nanotubes' conformational nonidealities, such as nanotube misalignment and aggregation/entanglement. Here we quantitatively investigate the interfacial load transfer in electrospun carbon nanotube poly(methyl methacrylate) (PMMA) nanocomposite microfibers by using in situ Raman micromechanical characterization techniques. The micromechanical measurements capture the critical tensile strain in the composite microfiber that initiates collective interfacial slip. The nanotube alignment inside the microfiber is characterized by using polarized Raman spectroscopy. The equivalent maximum interfacial shear stress in the tested nanotube-PMMA composite microfibers, which takes into account the nanotube alignment, is quantified using shear-lag micromechanics models and is found to be substantially lower than the reported values from single-nanotube pull-out measurements. The reported findings are helpful to better understand the effect of nanotube conformational nonidealities produced from processing on the interfacial stress transfer characteristics and the strengthening efficiency in nanotube-reinforced nanocomposites.