Scalable Manufacturing of Hierarchical Nanostructures

The focus of this thesis is a new simple and scalable process to make surface coatings that have multiple length scales, or hierarchical features. Typically, the formation of hierarchical structures involves multiple steps and/or long processing times. In this new process, the hierarchical geometry is formed in a single step. The starting material-spherical copper powder-is oxidized in ambient air. Depending on the starting size of the powder, copper oxide nanowires may or may not form. Systematic thermogravimetric analysis (TGA) and in-situ x-ray diffraction (XRD) studies provide insights into the size-dependent thermal oxidation process. The proposed mechanism is supported by another interesting geometrical transformation: in the same single-step process, a large void is formed in the particles. The tunable nanowire growth is used to make new kinds of hierarchical coatings with enhanced heat-transfer performance in spray-cooling applications, which include nuclear reactor boiling, continuous casting of metals, and thermal management of electronics. Thesis Supervisor: Kripa K. Varanasi Title: Doherty Chair in Ocean Utilization Associate Professor of Mechanical Engineering