Long-time translational self-diffusion in isotropic dispersions of colloidal rods

A dispersion of fluorescent colloidal silica coated boehmite rods with length $L\approx 325\mathrm{nm}$ and diameter $D\approx 46\mathrm{nm},$ dispersed in dimethylformamide, is synthesized. The concentration dependence of the long-time translational self-diffusion coefficient $D_s^L$ is measured with fluorescence recovery after photobleaching up to a rod volume fraction $\phi =\mathrm{0.22.}\mathrm{}$ A linear dependence of $D_s^L$ on concentration is found up to $\mathrm{}(L/D)\mathrm{}\phi =1.\mathrm{}$ At higher concentration $D_s^L$ levels off and decreases to 3% of its value at infinite dilution for $\mathrm{}(L/D)\mathrm{}\phi =\mathrm{1.5.}\mathrm{}$