Dynamic properties of aqueous dispersions of nanometric particles near the fluid–solid transition.

Here we investigate a colloidal suspension of practical interest, silica particles, which provides a mesoscopic system for the study of a dynamic near fluid–solid transition. Dynamic properties of concentrated solutions of nearly monodisperse charged colloids (standard deviation/mean radius≊0.11) at low ionic strength (≊6×10-4 M) have been studied by quasielastic light scattering. Below a volume fraction of the order of 15%, the solutions are viscous fluids and the refractive index fluctuations relax in two steps. Above a volume fraction of 20%, and over a macroscopic time window extending up to few seconds or more, the solutions are elastic and fluctuations in the refractive index become frozen. This is typical of systems which pass from a fluid to a solid state. The results are critically analyzed within the same framework used for similar macroparticle systems. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]