Slow dynamics of equilibrium density fluctuations in a supercooled colloidal liquid

On the basis of the recent theory for nonequilibrium suspensions of colloidal hard spheres, the nonlinear equation for the particle mean-square displacement M-2(t) is derived for equilibrium suspensions of colloidal hard spheres as dM(2)(t)/dt = 6D(S)(L)(phi) + 6[D-S(S)(phi) - D-S(L)(phi)] exp[ - lambda(phi )M-2(t)], where phi is a volume fraction of identical hard spheres, D-S(S)(phi) and D-S(L)(phi) are short- and long-time self-diffusion coefficients, respectively, and lambda(phi) is a free parameter to be determined. This equation is used to analyze the recent experimental data for equilibrium colloidal suspensions with small polydispersity. By treating phi and lambda as free fitting parameters, a simple transformation from the theoretical volume fraction phi to the experimental volume fraction phi (exp) is obtained. The long-known phenomena similar to those in glass-forming materials, such as the alpha and beta relaxation processes, are also found. With increasing volume fraction phi (exp), we then observe a progression from normal liquid, to supercooled liquid, and to glass without any sharp transitions in lambda and D-S(L). Thus, analyses show that no divergence of the alpha- and beta -relaxation times take place although the dynamic properties of the colloidal liquid show a drastic slowing down in a supercooled region. (C) 2001 Elsevier Science B.V. All rights reserved.