Adhesive Energy of Zinc Oxide and Graphite, Molecular Dynamics and Atomic Force Microscopy Study
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Adhesive Energy of Zinc Oxide and Graphite, Molecular Dynamics and Atomic Force Microscopy Study Ulises Galan,1 Henry A. Sodano2,3 1
School for Engineering of Matter, Transport and Energy, Arizona State University, USA Department of Mechanical and Aerospace Engineering, University of Florida, USA 3 Department of Materials Science and Engineering, University of Florida, USA 2
Abstract Molecular Dynamics (MD) simulations are performed to calculate the interfacial energy between zinc oxide (ZnO) and graphitic carbon for the study of solid–solid adhesion. The MD model consists of a ZnO slab and a single layer of graphitic carbon. The calculation was validated experimentally by atomic force microscopy (AFM) liftoff. A polishing process was applied to create a tip with a flat surface that was subsequently coated with a ZnO film allowing force displacement measurement on Highly Oriented Pyrolitic Graphite to validate the simulations. The MD simulation and AFM lift-off show good agreement with adhesive energies of 0.303 J/m2 and 0.261 ± 0.054 J/m2, respectively. Keywords: Molecular Dynamics, Atomic Force Microscopy, Interface Strength Corresponding author. [email protected] Introduction Recently Lin at el [1] employed zinc oxide (ZnO) nanowires (NWs) as an interphase between the carbon fibers and polymer matrix in fiber reinforced composites and demonstrated a more than two times increase in the interfacial shear strength compared to bare fibers. The research was extended to investigate the properties of ZnO NWs on aramid fibers [2] as well as to study the role of morphology in the interfacial, [3] ultimately achieving 3.27 times the interface strength offered by a composites grade epoxy. The results suggested that the adhesion of the ZnO NWs with the fibers was responsible for the improved interfacial shear strength. In this context, the study of the surface interactions between ZnO and carbon offers the potential for further enhancement to this system as well as the general problem of adhesion to graphitic surfaces. With the aim to better understand the mechanical properties between ZnO and carbon, we develop a MD model and validate the model with AFM lift off measurements from the surface of Highly Oriented Pyrolitic Graphite (HOPG) using a ZnO coated AFM tip. Experiments MD simulates the atomic interactions that govern the energetics and properties of a material by describing these interactions with a force field and assuming atoms as single points with a defined mass [4]. A range of material properties such as adhesion, diffusion, cracking, creep, etc. can be studied by applying the laws of classical mechanics, thus MD provides a tool to study systems at an atomic level. The attractive and repulsive forces that arise at the atomic scale are defined by a force field can be divided into bonded and non-bonded interactions for neutral systems, while ionic interactions are accounted for by the summation of the electrostatic energies. The ionic interactions in ZnO can be described by pairwise interactions with the
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