Long-time tracer diffusion of nonspherical brownian particles

The long-time tracer-diffusion properties of a nonspherical Brownian particle that interacts with a suspension of spherical particles are studied in terms of an idealized but nontrivial two-dimensional model system. For this system, the predictions of the generalized Langevin equation approach to tracer diffusion can be calculated, and compared with the (extrapolated) results of a computer simulation experiment. In the model, the nonspherical particle is represented by a rigid linear array of N(T) (=2 or 3) spherical particles with nearest-neighbor separation DeltaL. We calculate the long-time rotational and (transverse and longitudinal) translational diffusion coefficients. The theory is found to reproduce qualitatively and quantitatively the main features of the extrapolated results. Finally, we also present theoretical results that derive from still simpler approximate theoretical schemes.