CAREER: Scalable Manufacturing of Hierarchical Nanostructures by Acoustically Modulated Emulsion Technique for Next Generation Renewable Energy Applications

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Assembling nano building blocks into hierarchical structures can produce novel materials with unprecedented performance and functionalities, especially for next-generation renewable energy applications, including high-capacity batteries and high-efficiency solar cells, thus securing the energy future and prosperity of the nation. Existing methods to manufacture hierarchical nanostructures with long-range order require the use of templates that are limited in terms of fabrication scalability, cost, and time. They also lag behind on generating controlled composition variations in three-dimensional structures. This award supports fundamental research to produce needed knowledge for the study of a facile process to generate scalable and reconfigurable three-dimensional templates for the directed assembly of hierarchical nanostructures with rationally designed structure, topology, composition, and long-range order. This research promotes scientific understanding of the self-assembly process and provides strategies to direct the assembly by engineering the environment. Since assembly process is common in nature, e.g., living cells assemble into functional organs following a hierarchical order, knowledge from this research contributes to the understanding of life and life's engineering, which impacts the NSF Big Idea of 'Understanding the Rules of Life'. The multi-disciplinary research, involving acoustics, fluid dynamics, materials science and manufacturing, provides unique training and research opportunities to undergraduate and graduate students. The project involves community college students, especially, those from under-represented minorities, in research and help achieve academic success in science and engineering.The assembly of hierarchical nanostructures directed by acoustically-modulated emulsion can overcome several limitations existing assembly methods have, including disordered structures in long range, high cost, lengthy time, low scalability, and limited control of composition and anisotropy. However, fundamental scientific barriers are yet to be overcome to fully exploit the application potential of hierarchical nanostructures. This research is to fill the knowledge gap on the dynamics of nanoparticles and nanoparticle-loaded droplets in the Pickering emulsion system when subjected to a standing acoustic field. The project performs multi-scale molecular dynamics and finite element simulation, coupled with experimental validation, to investigate the dynamics of nanoparticles and emulsion droplets and delineate the effects of key process variables. Based on the fundamental studies, acoustically-modulated emulsion systems are designed and developed to manufacture a set of rationally designed metal oxide hierarchical nanostructures with structural, topological and compositional anisotropy in both nano- and micro- scales. Using titanium dioxide-based dye sensitized solar cell as a model device, the correlation of nano- and micro- scale structural and compositional anisotropy with the macroscale material properties and device performances are established.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.