title: Adhesive force measurement between HOPG and zinc oxide as an indicator for interfacial bonding of carbon fiber composites.
abstract: Vertically aligned zinc oxide (ZnO) nanowires have recently been utilized as an interphase to increase the interfacial strength of carbon fiber composites. It was shown that the interaction between the carbon fiber and the ZnO nanowires was a critical parameter in adhesion; however, fiber based testing techniques are dominated by local defects and cannot be used to effectively study the bonding interaction directly. Here, the strength of the interface between ZnO and graphitic carbon is directly measured with atomic force microscopy (AFM) using oxygen plasma treated highly oriented pyrolytic graphite (HOPG) and an AFM tip coated with ZnO nanoparticles. X-ray photoelectron spectroscopy analysis is used to compare the surface chemistry of HOPG and carbon fiber and to quantify the presence of various oxygen functional groups. An indirect measurement of the interfacial strength is then performed through single fiber fragmentation testing (SFF) on functionalized carbon fibers coated with ZnO nanowires to validate the AFM measurements. The SFF and AFM methods showed the same correlation, demonstrating the capacity of the AFM method to study the interfacial properties in composite materials. Additionally, the chemical interactions between oxygen functional groups and the ionic structure of ZnO suggest that intermolecular forces at the interface are responsible for the strong interface.
authors.affiliation: †Materials Science and Engineering, University of Florida, PO Box 116400, Gainesville, Florida 32611-6400, United States.
authors.forename: Brendan A
authors.initials: BA
authors.lastname: Patterson
authors.affiliation: §School for Engineering of Matter, Transport and Energy, Arizona State University, Mail Stop 6106, Tempe, Arizona 85287-6106, United States.
authors.forename: Ulises
authors.initials: U
authors.lastname: Galan
authors.affiliation: ‡Aerospace Engineering, University of Michigan, 1320 Beal Avenue, Ann Arbor, Michigan 48109-2140, United States.
authors.forename: Henry A
authors.initials: HA
authors.lastname: Sodano
keywords: ZnO nanowires; atomic force microscopy; composite interfaces; intermolecular interactions; oxygen functional groups