Slow dynamics of equilibrium density fluctuations in a supercooled colloidal liquid

On the basis of the recent theory for nonequilibrium suspensions of colloid al hard spheres, the nonlinear equation for the particle mean-square displa cement M-2(t) is derived for equilibrium suspensions of colloidal hard sphe res as dM(2)(t)/dt = 6D(S)(L)(phi) + 6[D-S(S)(phi) - D-S(L)(phi)] exp[ - lambda(ph i )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, respective ly, and lambda(phi) is a free parameter to be determined. This equation is used to analyze the recent experimental data for equilibrium colloidal susp ensions with small polydispersity. By treating phi and lambda as free fitti ng parameters, a simple transformation from the theoretical volume fraction phi to the experimental volume fraction phi (exp) is obtained. The long-kn own phenomena similar to those in glass-forming materials, such as the alph a and beta relaxation processes, are also found. With increasing volume fra ction phi (exp), we then observe a progression from normal liquid, to super cooled 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 -relaxat ion times take place although the dynamic properties of the colloidal liqui d show a drastic slowing down in a supercooled region. (C) 2001 Elsevier Sc ience B.V. All rights reserved.