Chemical Engineering Department Seminar

1. Is the lotus leaf truly superhydrophobic?
   This question was studied by observing water on lotus leaves and lotus-like surfaces at the micro- and macro-meter scales. Our work suggests that these surfaces can be either hydrophobic or hydrophilic. This finding may have significant ramifications on how to make and use “superhydrophobic” surfaces.
2. Nanocomposite coatings and nanowires by physical vapor deposition
   By co-deposition and controlled phase-separation, we have synthesized nanocomposite thin films with enhanced mechanical, tribological, and electrical properties. We have also demonstrated that the residual stress in the co-deposited films could be exploited to grow nanowires. These nanocomposite coatings and nanowires have applications in areas such as friction reduction, magnetic recording, and energy conversion and storage.
3. Understanding diffusion-induced-stresses in nanostructured materials for durable lithium ion batteries
   We examined the effects of surface tension and surface modulus on diffusion-induced stresses within spherical nano-particles. We showed that both the magnitude and distribution of stresses could be significantly affected by surface mechanics for nano-particles. In particular, a tensile state of stress may be significantly reduced in magnitude or even be reverted to a state of compressive stress with decreasing particle radius. This reduction in tensile stress may be responsible for the observed resilience to fracture and decrepitation of nanostructured materials used in electrochemical energy storage.   

These examples suggest a wide range of applications of nanostructured materials. They also illustrate the multidisciplinary nature of materials research.   

Biography: Y.-T. Cheng attended Peking University between 1978 and 1980 (Physics). He transferred to Caltech and received all his degrees there (B.S. (1982) in Physics/Math, M.S. (1983) and Ph.D. (1987) in Applied Physics). He was with General Motors R&D Center from 1987 to 2008, most recently as a Technical Fellow and a lab group manager responsible for engineered surfaces, tribology, and functional materials. In August 2008, he moved to the University of Kentucky as a professor of materials engineering. He has 28 US patents and over 100 publications in areas such as nanoindentation modeling and measurements of mechanical properties; growth, structure, and properties of nanostructured materials (e.g., amorphous materials, nano-composites, epitaxial single crystals, single crystal nanowires); microscopic shape memory and superelastic effects; superhydrophobic surfaces; magnetorheological fluids; ion-solid interactions and ion beam modification of materials; fuel cells and batteries; and environmentally friendly machining processes. He is a Fellow of the American Physical Society (APS) and a member of the Materials Research Society (MRS) and ASM International. Additional information may be found at: http://www.engr.uky.edu/~ycheng/.