A coupling model analysis of dynamics of concentrated colloidal suspensions

Recent dynamic light scattering measurement on concentrated suspensions of 'hard-sphere' colloidal particles by Segre and Pusey (1996, Phys. Rev. Lett., 77, 771) are compared with the theoretical results calculated by the coupling model. The calculated normalized intermediate scattering function decays exponentially at both short and long times, f(Q, short t) proportional to exp[-D-S(Q)Q(2)t] and f(Q, long t) proportional to exp [-D-L(Q)Q(2)t] respectively, with D-L(Q) and D-S(Q) having the same Q dependence. The ratio D-L(Q)/D-S(Q) decreases rapidly with volume fraction phi. At intermediate times, the decay of f(Q, t) is slower and nonexponential, becomes increasing slower and extends to longer times as phi increases. There is good agreement between theory and experiment. It is also pointed out that the diffusional dynamics found in concentrated colloidal suspensions are general and shared by other densely packed interacting systems.