High Interfacial Shear Strain in Polyurea-Carbon Nanotube Composite Sheets

One of the factors limiting the performance of polymer-carbon nanotube (polymer-CNT) composites is the insufficient load transfer across their interface. In this study, interfacial strain in polyurea-CNT systems with two types of CNT sheet has been studied. These are (a) as manufactured CNT sheets (termed unbaked CNT sheets) containing amorphous carbon and (b) thermally treated CNT sheets (termed baked CNT sheets) with amorphous carbon eliminated. The process of baking not only eliminates amorphous carbon but also creates chemically active defects in CNTs as well as sp³ carbon. These factors serve to enhance interfacial strain in the polyurea-CNT system. The shift in the Raman G′ band, while the sheets were mechanically strained, has been used to estimate the polyurea-CNT interfacial strain. The maximum Raman G′ downshift in the range of 33-39 cm^-1 has been observed in composites of baked CNT sheets with 53 wt % polyurea. This is more than a factor of 2 higher than the downshift reported for any polymer-CNT system to date and represents a local CNT strain of â'¼0.9-1% or a local CNT stress of 9-10 GPa. This study opens a window toward achieving the mechanical properties potential of bulk polymer nanocomposite for applications including, but not limited to, structural materials.