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

•Small silica spheres (18–56 nm in diameter) in water was focused.•Debye screening lengths were calculated from electrical conductivity.•Steady electrical double layers were confirmed by DLVO theory.•Deionized suspensions of 18-nm spheres showed a glassy property.

The rheological properties of aqueous suspensions of small silica spheres (18–56 nm 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, 29 nm and 56 nm in diameter, were Newtonian fluids at sphere volume fraction ϕ = 0.10, although the suspension of the smallest spheres, 18 nm, 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 18 nm, 29 nm, and 56 nm 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.

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