Diffusion of Rods in 3 Dimensions

Ken Desmond, David Kilgore, Vikram Prasad, and Eric Weeks

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We are interested in understanding the viscoelastic properties of many different types of materials such as polymers, gels, and biomaterials. Currently there are many techniques for measuring viscoelastic properties. For example, the viscosity of glycerol can be measured using a rheometer. The typical sample size for a standard rheometer is about 5mL which can be expensive and time consuming if we were to use this technique to measure the viscosity of a biomaterial. Instead of using a rheometry, there is a technique called two-particle microrheology which looks at the correlated motion of micron size particles suspensed in a sample. From the correlated motion of these particles one can determine specific viscoelastic properties. Curently, this technique only looks at the correlated motion of micron size spheres. We are extending this technique to also be able to measure viscoelastic properties from the correlated motion of rods suspended in a complex fluid. Our experiment consist of using a confocal microscope to track the 3 dimensional motion of rod-like bacteria suspended in a water glycerol mixture. Using a program called POV-ray and using the tracked positions and orientations of the bacteria I made a movie that can viewed by clicking the following link. Rods Movie. Or, click here to see a movie for red/blue 3D glasses.

If you want to learn more about microrheology, I've listed below a website that explains some of the basics.
Introduction to microrheology by Eric Weeks & Dave Weitz at Harvard University
See also our new movies of diffusing ellipsoids, taken by Ken Desmond.

For more information, please contact Eric Weeks: <weeks(at)physics.emory.edu>