Quantitative determination of size and properties of interphases in carbon nanotube-based multiscale composites

Experimental investigations are carried out to quantify the effect of filler composition, filler diameter and carbon nanotube (CNT) grafting on the properties of interphase in epoxy matrix composites. To this end, epoxy is reinforced with stainless steel (SS) wire, brass wire(s) and carbon fiber (CF) before and after CNT growth on their surface. Surface morphology, elemental composition and thickness of interphase in unsized (ar) and CNT grafted composites is studied using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The size and mechanical properties of the interphase are evaluated through nanoindentation and pull-out tests. It is observed that interphase properties depend on material and geometry of reinforcing filler. Moreover, CNT grafting on the filler surface improves the size and stiffness of interphase and increases the interfacial shear strength (IFSS). The relative improvement in interphase properties and IFSS due to grafting of CNTs on the surface of wires and carbon fiber found to be a function of interfacial chemistry between reinforcement and epoxy. SEM analysis of pulled out wires and fibers reveals that the interface fails differently in the presence and absence of CNTs on their surface. Moreover, increase in CNT growth time from 15 to 30 min inside chemical vapor deposition (CVD) reactor increases the interphase thickness but has an adverse effect on the IFSS in CF/epoxy composites. It is shown that the size and composition of reinforcement and grafting of CNTs on their surface are the variables which provide a handle to suitably design the interphase in multiscale composites. (C) 2018 Elsevier Ltd. All rights reserved.