Abstract
Recent dynamic light scattering measurement on concentrated suspensions of ‘hard-sphere’ colloidal particles by Segrè 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) ∞ exp [-D S(Q)Q 2 t] and f(Q, long t) ∞ exp [-D L(Q)Q 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 ϕ. At intermediate times, the decay of f(Q, t) is slower and non-exponential, becomes increasing slower and extends to longer times as ϕ 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.