Like likes like: counterion-mediated attraction in macroionic and colloidal interaction.

The colloidal and macroionic interaction is discussed within the mean-field approach. Bound pairs of latex particles are photographed at a low particle volume fraction of 10(-4). The effective pair-potential obtained therefrom has an attractive tail for highly charged samples, while no attraction is detected for a low-charge sample.

When, why, and how does like like like?: Electrostatic attraction between similarly charged species.

In the Derjaguin-Landau-Verwey-Overbeek (DLVO) framework of the past 60 years, colloidal interaction between similarly charged particles has been claimed to be simply repulsive, and an attraction such as the van der Waals interaction is attached to the Coulombic repulsion. Statistical-thermodynamic considerations show that the electrostatic Helmholtz free energy ΔF(el) is generally not equal to the electrostatic Gibbs free energy ΔG(el) for simple ionic solutions, and the difference ΔG(el) -ΔF(el) (corresponding to the electrostatic osmotic pressure p(el) ) becomes larger with increasing charge number. Thus, it is expected that ΔG(el) -ΔF(el) be large for highly charged macroions.

Rupture and regeneration of colloidal crystals as studied by two-dimensional ultra-small-angle X-ray scattering.

The structure of colloidal crystals of silica particles in water was studied by using the two-dimensional (2D) ultra-small-angle X-ray scattering (USAXS) technique. By violent shaking of the dispersion, large (body-centered cubic, bcc) crystals were broken into microcrystals while the lattice structure and lattice constant were preserved. The 2D-USAXS profiles revealed that the [111] direction of bcc microcrystals was parallel to the capillary axis and their orientational distribution with respect to the capillary axis was random.

Structure of colloidal crystals in sedimenting mixed dispersions of latex and silica particles.

We report bcc-fcc transitions of colloidal crystals in mixed aqueous dispersions of polystyrene-based latex particles (diameter: D=55.8 nm) and silica particles (diameter: D=170 nm). In the single systems, the silica particles formed bcc crystals and the latex particles did not crystallize.