Structural and dynamic properties of colloidal liquids and gases of silica spheres (29 nm in diameter) as studied by the light scattering measurements

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Static and dynamic light-scattering measurements are made for colloidal-liquids and -gases of silica spheres (29 nm in diameter) in the exhaustively deionized aqueous suspension and in the presence of sodium chloride. Single broad peak is observed in the light-scattering curve and the liquid-like and gas-like distributions have been observed. Colloidal crystals are not formed at any sphere concentrations. The nearest-neighbored interparticle distances of colloidal liquids, l obs , agree excellently with the effective diameters of spheres (d eff ) including the electrical double layers in the effective soft-sphere model and also with the mean intersphere distances, l o , calculated from the sphere concentration, i.e., l obs ≈d eff ≈ l o . This relation supports the importance of the electrostatic interparticle repulsive interaction. Two dynamic processes have been extracted separately from the time profiles of autocorrelation function of colloidal liquids. Decay curves of colloidal gases are characterized by the single translational diffusion coefficients, which are always lower than the calculation from the Stokes-Einstein equation using true diameter of spheres and increase as ionic concentration increases. These experimental results emphasize the importance of the expanded electrical double layers and the electrostatic intersphere repulsion on the structural and dynamic properties of the colloidal liquids and gases.