Experimental study for rheological property of exhaustively deionized aqueous suspension of very small colloidal spheres (diameter < ca. 60 nm)

Abstract

The rheological properties of aqueous suspensions of small silica spheres (18–56nm in diameter), in an exhaustively deionized state and the presence of a salt, have been investigated. In a deionized state, the suspensions of larger spheres, 29nm and 56nm in diameter, were Newtonian fluids at sphere volume fraction ϕ=0.10, although the suspension of the smallest spheres, 18nm, showed shear thinning at ϕ=0.087. Debye screening lengths were calculated based on electrical conductivity. The effective volume fractions, including the electrical double layers, of suspensions in the above condition were 0.37, 0.23, and 0.21 for spheres of 18nm, 29nm, and 56nm in diameter, respectively. Experiments provide strong evidence that all of the small spheres form steady electrical double layers in water and that the suspension of 18-nm spheres was in a glassy state.