Polymer nanocomposite – fiber model interphases: Influence of processing and interface chemistry on mechanical performance

Abstract

Electrophoretic deposition (EPD) has been established as a scalable and environmentally friendly approach for depositing carbon nanotubes (CNTs) from aqueous colloidal dispersions onto a variety of fibrous surfaces. EPD facilitates the micro/nano hybridization of CNTs and reinforcing fibers, enabling the controlled engineering of hierarchically-structured composites. Model studies have shown that the chemistry of the CNTs in the fiber/matrix interphase plays a critical role in the mechanical performance of the composite. Composite interphases were replicated on planar glass substrates to systematically study the influence of CNT functionalization, glass surface chemistry, and aqueous dispersion quality on the mechanical performance under shear loading. CNTs were functionalized using a novel ultrasonicated-ozonolysis (USO) and polyethyleneimine (PEI) process to prepare films on silane-treated glass surfaces. The epoxy-infused films exhibited a 50% improvement as compared to untreated glass/epoxy interfaces. Detailed surface analysis using X-ray photoelectron spectroscopy shows chemical bonds in the interphase, and computational modeling of the valence band spectra provides additional insight into the chemical nature of the bond. The formation of a PEI–CNT rich interphase facilitates a more homogeneous, ductile fracture zone relative to the brittle glass epoxy interface, and increases composite strength by shifting the fracture surface away from the glass surface. Intentional destabilization of the CNT dispersion resulted in re-agglomeration, diminishing any benefit of the PEI, thereby demonstrating the importance of a stable dispersion provided by the USO processing. The results replicate the trends observed previously in more complex composite systems and provide new insight into interfacial engineering of nanostructured composites.