Biomimetic Nanostructured Interfaces for Hierarchical Composites

Creating a hierarchical interface between the reinforcement and matrix phases of fiber reinforced polymer composites has become an effective strategy toward development of bioinspired structural composites. The resulting materials display exceptional characteristics such as having both high stiffness and high toughness simultaneously, which is rare in homogeneous materials. Although the efficacy of nanostructured interfaces has been established, the mechanisms associated with their performance have not been explored yet. Here, strain transfer across a nanowire interphase is visualized in order to understand the working principles of physical interface modifications. This is accomplished by using a functionally graded piezoelectric interface composed of nanowires, as their piezoelectric properties can be utilized to control the strain on one side of the interface. It is demonstrated that the nanowire “whiskers” cause an even strain transfer from the reinforcement phase into the matrix phase, eliminating stress concentration between the phases. The role of nanostructured interfaces in hierarchical fiber reinforced composites is studied through visualizing the strain distribution across a nanowire interphase. To represent this interphase, a functionally graded piezoelectric interface composed of vertically aligned lead zirconate titanate nanowires is utilized to precisely control the strain on one side of the interface. Results explain the physics behind the observed behavior of multiscale composites.