MULTIFUNCTIONAL COMPOSITES REINFORCED WITH FUNCTIONALIZED NANOMATERIALS: INTERPHASE CHARACTERIZATION AND APPLICATIONS

The current research explores a novel and industrially scalable processing technique to hybridize carbon nanotubes with traditional advanced fibers to prepare composites with multifunctional capabilities. High concentrations of carbon nanotubes (CNTs) have been integrated in fibrous preforms using an electrophoretic deposition (EPD) approach to produce composite materials with improved structural and functional performance. A stable aqueous dispersion of CNTs was produced using a novel ozonolysis and ultrasonication (USO) technique that results in dispersion and functionalization in a single step. Within the composite, networks of CNTs span between adjacent fibers, and the resulting composites exhibit significant increases in electrical conductivity and considerable improvements in the interlaminar shear strength and fracture toughness. In order to better understand the underlying mechanisms behind the selective reinforcement of CNTs on the glass-epoxy systems, model interphases were created on planar glass substrates and the surface chemistry and mechanical performance was characterized. The glass substrates were modified with a silane coupling agent followed by deposition of ozone and PEI functionalized CNTs. Lap shear joints were fabricated to examine the model interphase shear strength. Mechanical testing provided relative shear strength and failure representative of that occurring in a fiber composite. Chemical characterization of the failure surfaces using high resolution X-ray photoelectron spectroscopy (XPS) indicated increased shear strength occurred when fracture propagated in the CNT-rich interphase region between the glass and resin. Additionally, preliminary microdroplet debond tests have been conducted to investigate the interfacial properties between an epoxy matrix and E-glass fibers with the electrophoretically coated CNTs. The CNT-modified glass-fiber composites also exhibited electrical-resistance sensitivity to applied shear strain, with the rate of change dependent on the extent of plastic deformation, which enables damage sensing and structural health monitoring applications. The USO technique has also been applied to processing of exfoliated graphite and has enabled EPD of graphitic nanoplatelets onto E-glass fibers.