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Séminaire Tom Lubensky

On Rotational and Translational Brownian Motion


Tom C. Lubensky

Department of Physics and Astronomy
University of Pennsylvania

Einstein’s 1905 paper on Brownian motion ushered in a new era in statistical physics. It provided a description of the peculiar random motion of micron-sized particles dispersed in water in terms of collisions with much smaller water molecules and a prescription for determining Avogadro’s number through measurements (later carried out by Jean Perrin) of the mean-square displacement of the dispersed particles. Perrin’s measurements were instrumental in establishing the molecular nature of matter. In 1906, Einstein introduced the concept of rotational Brownian motion.

This talk will discuss recent experiments by the Penn group [1] on coupled translational-rotational Brownian motion of rigid rods and interpret them in terms of a Langevin theory originally developed by Francis Perrin (son of Jean Perrin). It will discuss in particular crossover from anisotropic to isotropic diffusion and non-Gaussian probability distributions. Finally it will generalize concepts of rotational Brownian motion to treat the dynamics of a non-equilibrium granular gas of chiral objects.

[1] Han, Y., Alsayed, A. M., Nobili, M., Zhang, J., Lubensky, T. C., and Yodh, A. G., Brownian Motion of an Ellipsoid, Science 314, 626-630 (2006).