Visualization of dislocation dynamics in colloidal crystals

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Zach Wissner-Gross (April 14, 2009)


Visualization of dislocation dynamics in colloidal crystals

Peter Schall, Itai Cohen, David A. Weitz, and Frans Spaepen

Science, 2004, 305, 1944-1948

Soft matter keywords

Crystal defects (dislocations), colloidal crystals, continuous and discrete models


Crystal defects have physical consequences at multiple length scales: the structure of the dislocation itself depends on interatomic potentials; interactions between dislocations results in forces on the mesoscopic scale; and finally, macroscopic crystal deformation depends on the dislocations as well. The authors point out the difficulty in being able to observe all these length scales simultaneously, to gain a more complete understanding of crystal defects.

But why not simply scale everything up a few orders of magnitude, using colloidal crystals (with colloids as the repeating units, rather than atoms)? While the interactions between colloids may not be exactly the same as those between atoms, the authors state that colloid crystals can make a good model for crystals in general, and go on to study dislocations in colloid crystals at multiple length scales.

Using a laser scanning confocal microscope to determine the positions of individual colloid particles (Figure 1), along with laser diffraction microscopy to detect dislocation structure and growth (Figure 2), the authors present several new findings, most notable of which is that the continuum model for crystal defects yields good physical approximations, even for crystals too thin to be considered good candidates for the model.

Soft matter discussion

Not being particularly familiar with dislocation mechanics, I will admit I had a difficult time understanding the authors' discussion of Burgers vectors and Shockley partials.