ZnO Nanostructured Interphase for Multifunctional and Lightweight Glass Fiber Reinforced Composite Materials under Various Loading Conditions

The optimal mechanical performance of glass fiber reinforced epoxy matrix composites typically relies on the suitability of its interfacial properties to the applied loading conditions. The contrasting interfacial requirements for glass fiber composites in ballistic versus structural applications require multicomponent designs that lead to an increase in the system’s weight, cost, and complexity. Thus, interfacial modifications that yield a multifunctional composite performance are necessary to simultaneously yield maximal energy absorption under dynamic loading rates and high resistance to delamination under static loading rates. In this work, a zinc oxide (ZnO) nanostructured interphase is grafted on the surface of glass fibers to enable the tuning of interfacial shear strength (IFSS) in glass fiber reinforced composites (GFRC) for optimal behavior across a large range of strain rates. The glass fibers are functionalized by using a treatment in piranha solution to increase the surface oxygen content and improve the adhesion between the fiber and the ZnO nanostructure. The ZnO nanowires displayed up to 96% improvement in average IFSS relative to untreated fibers at a quasi-static strain rate and a 68% decrease in IFFS compared to untreated fibers at strain rates greater than 2000 s^–1. The enhanced average IFSS at static loading conditions is caused by the creation of a functional gradient at the glass fiber–epoxy matrix interface due to the ZnO nanowire interphase, while the decrease in interfacial properties at dynamic loading rates is the result of matrix stiffening, causing brittle fracture of the ceramic interphase. These results demonstrate the potential of integrating ZnO nanomaterials at the fiber–matrix interface to simultaneously introduce ballistic and structural functionality into fiberglass reinforced polymer matrix composites.