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 Deltax(t) in time t, by D(n)[triple bond]<[Sigma(i=1)(n)Deltax(i)(t)](2)>/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 D(n) on colloid packing fraction. We find that the ratio of D(n) to the infinite dilution self-diffusion coefficient D(S)(0) increases as n increases, eventually saturating for large n. The observed dependence of D(n) on n is in satisfactory agreement with the predictions obtained from both Stokesian dynamics simulations and hydrodynamic calculations using the method of reflections.