ChBE Seminar Series: Daeyeon Lee
Tuesday, March 5, 2013
Room 2108 Chemical and Nuclear Engineering Bldg.
Professor Kyu Yong Choi
Enhancing the Assembly and Properties of Nanoparticle Films
Department of Chemical and Biomolecular Engineering
University of Pennsylvania
Nanoparticle films (NFs) composed of multiple nanomaterials have synergistic functionality, making them useful in numerous advanced applications including energy storage and conversion. Widespread use and commercialization of NFs, however, are hampered by difficulty associated with generating defect-free films with high mechanical robustness and durability. In this talk, I will discuss our recent efforts to generate crack-free NFs and to improve their mechanical properties. A new method utilizing subsequent depositions of thin crack-free nanoparticle layers is demonstrated to avoid the formation of cracks within silica nanoparticle films. Using this method, NFs can be assembled with thicknesses exceeding the critical cracking values. Application of this method for fabricating crack-free functional structures is demonstrated by producing crack-free Bragg reflectors, which we use to enhance the power conversion efficiency of a dye-sensitized solar cell (DSSC). In the second part of the talk, I will describe our recent efforts to enhance the mechanical properties of NFs using atomic layer deposition (ALD). We demonstrate that the mechanical properties of NFs can be drastically enhanced at a relative low temperature without compromising the intrinsic functionality of the NFs. Our results demonstrate that the mechanical properties of ALD-reinforced NFs are dominantly influenced by the mechanical properties of the ALD materials rather than by the compositional matching between ALD and nanoparticle materials. In the last part of this talk, I will describe our recent efforts to understand the effect of particle geometry on the mechanical properties and failure of NFs. While the mechanical properties of NFs depend strongly on the volume fraction of the films, their failure mechanism is significantly influenced by the shape of nanoparticles that composes the NFs.