Mechanics of Energy Storage Materials
Developing lithium ion batteries with higher energy density is considered to be an important challenge of our times in order to enable electric vehicles that can compete and hopefully replace internal combustion engine driven vehicles. Developing the next generation of Li-ion batteries requires designing new anodes, cathodes and electrolytes that can survive thousands of charge-discharge cycles with minimal capacity fading. Stresses in the electrode materials not only determine the mechanical integrity & cycle life, but also influence the electrochemical performance. It is essential to understand the mechanics of damage evolution in the electrode materials in order to develop predictive models to help battery designers in arriving at optimal material designs.
Motivated by such practical applications, we pursue a number of exciting problems at the interface between solid mechanics and chemistry. For example, we recently demonstrated the role of plastic deformation on the energy recovery efficiency of silicon based anodes; coupling between stress and electric potential in silicon; and the evolution of mechanical properties of silicon as a function of Li concentration. A number of other related phenomena are under current investigation. Primary funding for this effort comes from the DOE EPSCoR Implementation grant (PI: Guduru) and NASA. Additional support is provided by Argonne National Laboratory, NSF (MRSEC) and the State of Rhode Island.
- V.A. Sethuraman, M.J. Chon, M. Shimshak, V. Srinivasan, P.R. Guduru, "In Situ Measurements of Stress Evolution in Silicon Thin Films during Electrochemical Lithiation and Delithiation", J. Power Sources 195, 5062-5066, 2010.
- V.A. Sethuraman, V. Srinivasan, A.F. Bower, P.R. Guduru, In situ Measurements of Stress-potential Coupling in Lithiated Silicon", J. Electrochem. Soc., in press (2010).
- A.F. Bower, P.R. Guduru, V.A. Sethuraman, "A Finite Strain Model of Stress, Diffusion, Plastic Flow and Electrochemical Reactions in a Lithium-ion Half-cell", Submitted to J. Mechanics and Physics of Solids (2010).
- V.A. Sethuraman, M. Shimshak, M.J. Chon, N. Van Winkle, P.R. Guduru, "In Situ Measurement of Biaxial Modulus of Si Anode for Li-ion Batteries", submitted to Electrochemistry Communications (2010).
Stress-controlled Catalysis via Engineered Nano-structures
This project aims to develop a scientific basis for controlling chemical reactions using applied stress, with particular application to catalytic processes. Enhanced control of chemical reactions has enormous and broad implications for energy generation and conversion, chemical synthesis, sensing, and material degradation. The use of mechanical stress or strain to augment traditional alloying methods provides an avenue both for fine-tuning reaction specificity and/or selective and active control during chemical processes. The current effort attempts to demonstrate that active control using cyclically-applied stress can alleviate the well-established “volcano” effect wherein a desired reaction is optimal only in a narrow operating window due to competing reactions, and thereby overcome what has been believed to be a fundamental limiting factor in design of catalytic systems. The scientific underpinning will be demonstrated by developing two general platforms (thin films and nano-pillars) that can sustain high mechanical loading while also accommodating a range of material systems and catalytic reactions. Guidance for the choice of materials, the qualitative role of applied stress, and the characterization of reaction pathways, will be provided by modeling using quantum mechanics methods within novel multiscale simulation environments that can enable control of the mechanical loading and geometry effects. We hope to demonstrate unambiguously that stress can be used to substantially modify and control chemical reactions, along with possible engineering paths, via both thin film and bulk metallic glass nanostructures, for implementing stress control across a wide material space. This effort is supported by an ARO-MURI grant and is at an initial stage and rapidly gaining momentum. Stay tuned for publications in near future.
Biologically Inspired Contact Mechanics
The ability of small animals such as insects, flies and geckos to climb up vertical walls and to walk up side down on ceilings has been a subject of active research in biology for many centuries. There are a variety of mechanisms employed by these animals, including tiny claws, adhesive secretions, smooth and hairy adhesive pads, etc. Following the accumulation of a large body of anatomical and functional data on various natural adhesion systems, in the last few years biologists and engineers have been working together to develop a quantitative understanding of various natural adhesion and friction systems. This is a growing field of research with a rich set of challenging problems at the interface between biology, applied mechanics and micro/nano-fabrication, with potentially significant benefits if we can understand and mimic some of nature's optimized solutions to develop useful technologies.
The focus of this research is on engineering the topography of surfaces at micron and nano scale in order to understand the mechanics of biological adhesion and friction systems; and to develop biomimetic strategies which implement nature's mechanisms for adhesion and friction. Such a study naturally leads to several basic mechanics problems in rough surface adhesion and friction of soft materials, which we study in our lab. Some of the specific problems being addressed are: Mechanics of direction dependent friction (Friction Anisotropy) exhibited by biological surfaces and implementing such strategies on laboratory surfaces; Mechanics of roughness induced instabilities at nano and micron scales; Optimal design and fabrication of nano-hairy surfaces. The key idea is to manipulate surface topography at nano and micron scale to tailor macroscopic adhesion and friction properties; not surface chemistry. Funding sources: Air Force Office of Scientific Research (AFOSR) and National Science Foundation.
- J.F. Waters, P.R. Guduru. Mode-mixity-dependent adhesive contact of a sphere on a plane surface. Proceedings of the Royal Society of London, A. doi:10.1098/rspa.2009.0461. 2009.
- J.F. Waters, S. Lee, P.R. Guduru. Mechanics of axisymmetric wavy surface adhesion: JKR-DMT transition solution. International Journal of Solids and Structures 46: 1033-1042, 2009.
- H. Yao, S. Chen, P.R. Guduru, H. Gao. Orientation-dependent adhesion strength of a rigid cylinder in non-slipping contact with a transversely isotropic half-space. International Journal of Solids and Structures 46: 1167-1175, 2009.
- H. Yao, P.R. Guduru, H.J. Gao. Maximum strength for intermolecular adhesion of nanospheres at an optimal size. Journal of the Royal Society of Interface 5: 1363-1370, 2008.
- H. Yao, G. Della Rocca, P.R. Guduru and H. Gao. Adhesion and Sliding Response of a Biologically Inspired Fibrillar Surface: Experimental Observations. Journal of the Royal Society Interface. 5: 723-733, 2008.
- P.R. Guduru. Detachment of a Rigid Solid from a Wavy Elastic Surface - Theory. Journal of the Mechanics and Physics of Solids 55: 445-472, 2007.
- P.R. Guduru and C.Bull. Detachment of a Rigid Solid from a Wavy Elastic Surface - Experiments. Journal of the Mechanics and Physics of Solids 55: 473-488, 2007.
Guided Assembly of Nano-structures
Fabricating ordered patterns of controlled shape, size and spacing at nanoscale has been an important goal of nano-scale science and engineering during the past decade. Applications envisaged for such processes include quantum dot devices, nanocomposites, high density data storage devices, etc. Most of the existing nanofabrication techniques can be loosely described as either top-down type or bottom-up type. The top-down approach consists of examples such as photolithography, X-ray lithography, scanning probe/e-beam lithography etc. On the other hand, in the bottom-up approach, one tries to exploit certain configurational forces acting at nanoscale to drive a self-assembly process. However, there are a number of issues associated with the "self-assembly" route of fabricating devices of practical utility. For example, in case of strain driven quantum dot growth in semiconductor thin films, the resulting nanostructures usually do not possess any spatial order and also end up with a non-uniform size distribution. The objective of this work is to develop nanofabrication techniqes that combine the driving configurational forces that underlie self-assembly processes and the spatial control that can be achieved in top-down processes, in order to realize any desired spatial pattern and size distribution of nanostructures. We employ "very strong" electric and magnetic fields at solid surfaces to induce diffusion and patterning. Funding source: National Science Foundation.
- V. Gill, P.R. Guduru and B.W. Sheldon. Electric Field Induced Surface Diffusion and Micro/Nano-scale Island Growth. International Journal of Solids and Structures. 45: 943-958. 2008.
- V. Gill, "An Investigation of Electric Field Induced Surface Diffusion and Micro/Nano Scale Island Growth: Experiments and Modeling." Ph.D. Thesis, Brown University, 2008.
Mechanics of Nano-scale Structures
Research on the mechanics of carbon nanotubes has been dominated by modeling and computational simulations, primarily due to the extreme difficulty involved in performing controlled experiments on such small structures. The goal of this work is to develop new nanoscale experimental techniques to apply controlled force on individual nanotubes, measure the deflection at nanometer resolution and develop mechanics models to describe the experimental observations. We have developed an experimental technique to study shell buckling in individual multiwalled carbon nanotubes and showed that the measured buckling force is substantially higher than that predicted by the existing models. Motivated by these experimental observations, improved shell theories are being developed. Funding source: Air Force Office of Scientific Research (AFOSR).
- Z. Xia, P.R. Guduru and W. Curtin. Enhancing Mechanical Properties of Multi-Wall Carbon Nanotubes via sp3 Inter-wall Bridging. Physical Review Letters 98: Art. No. 245501, 2007.
- P.R. Guduru and Z. Xia. Experiments and Analysis of Buckling in Imperfect Multiwalled Carbon Nanotubs (Invited contribution to a special volume on novel testing techniques at nanoscale). Experimental Mechanics 47: 153-161, 2007.
- J.F. Waters, P.R. Guduru and J.M Xu. Nanotube Mechanics – Recent Progress in Shell Buckling Mechanics and Quantum Electromechanical Coupling. Composites Science and Technology. 66: 1141-1150, 2006.
- J.F. Waters, P.R. Guduru, T. Hanlon, M. Jouzi, J.M. Xu and S. Suresh. Shell Buckling of Individual Multi-walled Carbon Nanotubes Using Nanoindentation. Applied Physics Letters 87: 103109. 2005.
- J.F. Waters, L. Riester, M. Jouzi, P.R. Guduru and J.M. Xu. “Buckling instabilities in multiwalled carbon nanotubes under uniaxial compression.” Applied Physics Letters, 85: 1787- 1789, 2004.
Mechanical properties of biological tissues
It is known that the mechanical properties of biological tissues are influenced by their structure, bio-chemistry, history of past loading, pathology and genetics. Hence, accurate characterization of the properties provides a useful tool for biologists and physicians in assessing the health and recovery of tissues. In this work, we work with partners from Rhode Island Hospital and the Division of Biology and Medicine in developing characterizations techniques for tissues whose properties range from “gel-like” to “bone-like.” Funding source: National Science Foundation and NIH (COBRE).
- Middleton KM, Goldstein BD, Guduru PR, et al. Variation in within-bone stiffness measured by nanoindentation in mice bred for high levels of voluntary wheel running Journal of Anatomy, 216 (1): 121-131, 2010.
- J.M. Johnson, P.R. Guduru, K. Myers, et al. Measurement of the stress relaxation response to tension in the pregnant rat cervix, Reproductive Sciences, 15 (2) p. 263A-263A, 2008.
- K.M. Middleton, T. Garland, B.D. Goldstein, P.R. Guduru, S.A. Kelly, S.M. Swartz. Within-bone variation in stiffness measured by nanoindentation in high-running mice. Integrative and Comparative Biology 46: E98-E98, 2006.