The transition from a fluid to solid state is investigated by studying the viscosity of concentrated noncolloidal monodisperse and bidisperse suspensions of hard spheres. The notion of a range of fluidity limits, analogous to glass transition densities, is introduced. Lower bounds to this range are determined and compared with dry random close packings of the spheres. The ratio of the random-close-packing fraction to the lower bound fluidity limit of the bidisperse suspensions is found to be the same as for monodisperse spheres, a constant of 1.19, suggesting a random structure at this limit.

• Received 14 August 1991

DOI:https://doi.org/10.1103/PhysRevLett.68.1422