$199,994; NSF Engineering Research Initiation (ERI)

Increasing the Fundamental Understanding of the Auxetic Behavior of Graphene Oxide Membranes
Principal Investigator: Yijing Stehle, assistant professor of mechanical engineering and co-director of nanotechnology

When a material is stretched in one direction, it is typical for the dimensions in the other directions to decrease. However, some advanced materials, known as auxetic materials, exhibit a cross-sectional expansion that is perpendicular to the force applied during stretching. Auxetic materials are currently used in applications including body armor, packing materials, knee and elbow pads, and sponge mops. Graphene oxide membranes are a material with auxetic behavior, which makes them excellent candidates for a wide range of separation and filtration applications in the biomedical, automobile, and defense industries. However, there is still a limited understanding of the underlying mechanisms of their auxetic behavior. PI Stehle will carry out a series of experiments designed to gain a deeper understanding of the structure of graphene oxide membranes that causes its auxetic behavior. Additionally, through this project, the PI will provide research experiences for 2-4 undergraduates each year and will introduce additional students to this work, as well as solving engineering problems from a materials point of view, by integrating aspects of this research into laboratory-based courses.

The overall objectives of this project are to: 1) achieve a fundamental understanding of the auxetic behavior of graphene oxide membranes by conducting experiments based on two hypotheses – the wrinkle and/or the auxetic framework – are responsible for the behavior and 2) investigate how negative Poisson ratio customization affects the mechanical properties, stability, permeability, and potential applications of the membranes. By combining experimental studies and dynamic analyses, PI Stehle aims to not only identify the structural basis of graphene oxide membrane's auxetic behavior, but also devise techniques for customizing this behavior to address a range of engineering challenges.