The interphase microstructure and electrical properties of glass fibers covalently and non-covalently bonded with multiwall carbon nanotubes

We report on a solution-based method for the chemical grafting of multiwall carbon nanotubes (MWCNTs) onto the surface of glass fibers (GFs). MWCNTs and GFs were modified to expose the functional moieties for the formation of an 'amide' chemical bond. Treatment with strong acids introduces carboxylic groups to the MWCNT outer walls, which are converted to carbonyl chloride groups. The GFs are coupled with gamma-aminopropyltriethoxysilane (γ-APS) yielding amine surface functionalities (GF-APS), and acyl chloride modified MWCNTs (MWCNT-COCl) are covalently bonded in a dip-coating deposition process. The surface morphology and electrical properties of single fibers grafted with CNTs (GF-g-CNT) are studied and compared to physically adsorbed ones (GF-ad-CNT). The GF-g-CNT exhibited a fully CNT surface coverage and ten times higher electrical conductivity compared to the GF-ad-CNT. X-ray photoelectron spectroscopy (XPS), scanning electron and atomic force microscopy (SEM, AFM) were used to characterize the fibers after each step of treatment. Single filaments were embedded in an epoxy matrix to investigate the interphase microstructures, through transmission electron microscopy (TEM). Single-fiber pull out (SFPO) tests accompanied with fractographic analysis of the pulled-out fibers were performed to study the interfacial adhesion strength. The results suggest that GFs with chemically grafted MWCNTs are promising multi-functional reinforcements.