Spreading of colloid clusters in a quasi-one-dimensional channel

The effect of hydrodynamic interactions on the spreading of clusters of colloid particles in a quasi-one-dimensional channel is analyzed both experimentally and theoretically. An n-particle cluster spreading diffusion coefficient is defined, in terms of the displacement Delta x(t) in time t, by D-n /2nt, where the average is taken over all groups of n adjacent particles. Our study focuses on the n-dependence of D-n with some attention to the dependence of Dn on colloid packing fraction. We find that the ratio of Dn to the infinite dilution self-diffusion coefficient D-S(0) increases as n increases, eventually saturating for large n. The observed dependence of Dn on n is in satisfactory agreement with the predictions obtained from both Stokesian dynamics simulations and hydrodynamic calculations using the method of reflections. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3330414]