Role of Surface Chemistry in Adhesion between ZnO Nanowires and Carbon Fibers in Hybrid Composites

Abstract

Low interface strength is a persistent problem in composite materials and cascades to limit a variety of bulk material properties such as lamina shear strength. Whiskerization has long been pursued as a method to reinforce the interphase and improve both the single fiber interface strength as well as the bulk properties. Recent developments have shown that ZnO nanowire whiskerization can effectively improve the properties of a bulk composite without requiring the high temperatures that previous deposition processes needed. Although the efficacy of a ZnO nanowire interphase has been established, the mechanism for adhesion of the interphase to the fiber has not been identified. Specifically, the addition of the ZnO nanowires to the surface of the fibers requires that the ZnO nanowires have strong chemical adhesion to the fiber surface. This work will create a variety of chemical environments on the surface of the fibers through new and common chemical functionalization procedures and quantify the surface chemistry through X-ray photoelectron spectroscopy. The effect of fiber surface chemistry on the adhesion of the ZnO is assessed through single fiber fragmentation testing. The interface strength is found to strongly correlate with the concentration of ketone groups on the surface of the fibers. Following the experimental observations, liftoff of a ZnO crystal from a graphene surface was simulated with a variety of surface functionalizations. The computational models confirm the preference for ketone groups in promoting adhesion between ZnO and graphite.

Recent advances in fiber/matrix interphase engineering for polymer composites

“…This approach has been followed by the group of Ehlert [78,79]. These authors have created ZnO nanowire arrays on the surface of various reinforcing fibers, such as AF and CF.…”

“…Recall that a reduction in the fiber tensile strength is a common undesired "side-effect" of CVD treatments. This ZnO "nanowire whiskerization" was also adapted to CF [79]. The CFs were subjected to various surface treatments to produce functional groups, the presence of which was attested by XPS analysis.…”

STIR: Tailored Interfaces for High Strength Composites Across Strain Rates

“…It was recently found that the presence of ketones on the fiber surface may be desirable and thus a new functionalization process was developed here that employs a Friedel-Crafts reaction to graft chloroacetone to the fiber surface. 17 …”

“…4,16,17 In this test, a single fiber is embedded into a larger dogbone-shaped polymer specimen that is loaded while being observed through an optical microscope. As the specimen is stretched, the fiber will begin to break.…”

Biomimetic Nanostructured Interfaces for Hierarchical Composites

“…[20][21][22][23][24][25][26] The existence of CNTs, SiC, and ZnO nanostructures at the interface in a hierarchical fashion provides advanced hybrid composites with enhanced structural properties in comparison to conventional two-phase CFRP composites. A variety of composite materials with enhanced interfacial shear strength, [ 17,[19][20][21][22][23] vibrational damping, [ 24,[27][28][29] and interlaminar fracture toughness [ 15,18,[30][31][32] have been developed using this methodology. In these composites, the nanostructure interface bridges the reinforcement phase and pure polymer matrix phase-phases that generally have a largely mismatched elasticity.…”