| Popis: |
The coupling of Brownian rotation with sideways drift of nonspherical particles sedimenting in response to an external force Fex results in an effective translational diffusion over and above the Brownian translational diffusion. This paper considers particles possessing an axis of symmetry and a plane of symmetry normal to this axis. The effective translational diffusivity in a plane perpendicular to the external force is shown to be D EFF = Fex2(f1−1 − f2−1)2/64 D R, where f1 is the friction coefficient for translation along the axis of symmetry, f2 is the friction coefficient for translation normal to the axis of symmetry, and D R is the rotary diffusion coefficient. Because of fluctuations of velocity in the direction of Fex with fluctuations in orientation, there is also an effective translational diffusivity for this direction over and above the Brownian translational diffusivity; this is found to be twice the lateral diffusivity. Values of D EFF/ D , where D is the Brownian translational diffusion coefficient, have been computed for particles of several shapes. For example, a cylinder of length L very much greater than its radius yields D EFF/ D = (FexL/32kT)2. |
