Robert C. Cammarata Memorial Lecture: Frans Spaepen

Description

Frans Spaepen, a professor of applied physics in the School of Engineering and Applied Sciences at Harvard University, will give the inaugural Robert C. Cammarata Lecture titled "Why Ultrasoft Colloidal Crystals Are Really Very Strong" for the Department of Materials Science and Engineering.

Abstract:

Colloidal systems consist of micrometer-size spheres suspended in a liquid. They closely mimic atomic systems, in that they form similar phases (liquids, crystals and glasses) and exhibit similar dynamics, such as, for example, dislocation motion and crystal nucleation. By tracking the particles by confocal microscopy it is possible to observe these complex dynamic phenomena down to the particle, i.e. atomic, level, in three dimensions and in real time.

This talk will start with an introduction to the thermodynamic (equation of state) and mechanical properties (elastic moduli, lattice defects) of hard-sphere colloidal crystals. Two aspects will be explored in detail: (i) the growth of epitaxial single crystals and the relaxation of the associated stresses by misfit dislocations, and (ii) the stress-strain behavior during the shear deformation of a single crystal. The latter experiments show that these crystals exhibit classical work hardening and a remarkably high normalized strength.