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Join the Department of Mechanical Engineering for the 22nd annual James F. Bell Memorial Lecture in Continuum Mechanics. Frans Spaepen, the John C. and Helen F. Franklin Professor of Applied Physics at Harvard University, will present “Mechanical Properties of Colloidal Crystals.” The lecture begins at 3 p.m. in 210 Hodson Hall on Thursday, October 27. A reception will follow in the second floor lobby area of Hodson Hall.
Colloidal particles in suspension can form liquid, crystalline and glassy phases similar to those formed by atoms. Since the particles are “fat” (~1µm) and “slow” (~0.1s), they can be individually tracked in space and time by confocal microscopy. Dense colloidal systems therefore serve as “analog computers” to study the mechanics of crystals and glasses. Colloidal crystals and glasses have small (~ mPa) but non-zero elastic constants of largely entropic origin, which can be measured in a number of ways, for example from thermal fluctuations or variations in lattice constant. The non-zero stiffness of these phases creates elastic stress fields that can interact. This will be illustrated by observations of the nucleation and propagation of misfit dislocations during the epitaxial growth of colloidal single crystals. Nucleation and propagation of dislocations upon plastic deformation, such indentation, as well as their interaction with grain boundaries can be observed directly. By measuring the local strain fields in glasses, the Eshelby-like shear transformations that govern plastic deformation in these structures can be identified, and their dynamics can be observed directly.
Frans Spaepen is the John C. and Helen F. Franklin Professor of Applied Physics at Harvard University. He received his undergraduate degree in Metallurgical Engineering at the K.U. Leuven in 1971, and a PhD in Applied Physics from Harvard University in 1975. He joined the faculty of the Division of Applied Sciences at Harvard in 1977 as Assistant Professor, was appointed Associate Professor in 1981, and Full Professor in 1983. From 1990 till 1998 he was Director of the Harvard Materials Research Laboratory/Materials Research Science and Engineering Center. From 2002 to 2013 he was the Director of the Rowland Institute at Harvard. In 2008-9 he was Interim Dean of the School of Engineering and Applied Sciences and in 2009-10 Interim Director of Center for Nanoscale Systems. His research interests span a wide range of experimental and theoretical topics in materials science, such as amorphous metals and semiconductors (viscosity, diffusion, mechanical properties), the structure and thermodynamics of interfaces (crystal/melt, amorphous/crystalline semiconductors, grain boundaries), mechanical properties of thin films, the perfection of silicon crystals for metrological applications, and colloidal systems as models for the study of dynamics and defects in crystals and glasses.