Colloids as Models for Crystals and Glasses

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****TECHNICAL ABSTRACT****Suspensions of colloidal particles, with well-controlled size and interactions, will be used to study complex structures, defects and transformations in crystals and glasses. The motion of these particles can be tracked in space and time with high precision using confocal microscopy. The analogy between these particles and individual atoms will make it possible to obtain unique visual access at the particle/atomic scale to complex processes, such as the formation of crystal nuclei in a supercooled liquid, the nucleation of a melt in a superheated crystal, the interaction of dislocations with other defects, the structure and motion of grain boundaries, and the nature and kinematics of the shear transformation zones that govern plastic flow of simple glasses. This work aims to contribute to the fundamental science of materials and will give new impetus to long-standing "hard problems" in the field, such as nucleation and glass science. The work is uniquely interdisciplinary, in that it combines two areas with their own unique perspective: expertise in materials science complemented by that in colloid science. The work will provide a very rich learning environment, not only for broadly-trained graduate students in materials science, but also for research projects at the undergraduate or even high-school level.****NON-TECHNICAL ABSTRACT****Physical modeling of atomic-scale processes has a long and venerable history in materials science. In the 1940s, for example, the deformation of two-dimensional hexagonal raft of soap bubbles provided convincing evidence for the role of dislocations in plastic deformation of metals. We can now do this in three dimensions. The arrival of confocal microscopy has made it possible to track hundreds of thousands of colloidal particles in a suspension in time and space. By arranging this particles into crystalline or glassy structures, similar to those formed by atoms, we can now make "movies" of the formation or straining of these structures , and thereby obtain a unique view of these complex processes on the atomic/particle scale. An example is the growth of small crystal from a liquid during solidification, which appears to be much more complex than the simple growth of sphere that most theories have been assuming so far. Another example is the deformation of glasses, which have a non-periodic structure, and appear to deform by the rearrangement of pockets of about a hundred atoms; the colloid technique will allow a detailed look at the number, size and motion of these pockets. Both these phenomena -- nucleation and glass science -- represent long-standing "grand challenges" in materials science, to which this unique, interdisciplinary approach should provide new insights and impetus. This work will provide a very rich learning environment for the training of broadly educated graduate students. At the same time, the direct, visual nature of the work makes it highly accessible to younger students, even at the high-school level.