1989 Volume 17 Issue 2 Pages 116-122
Colloidal particles show some extraordinary behavior in their structural properties when they are in deionized suspension. In this article, some typical properties are reviewed. (1) Microscopic observation of crystal-like structures of spherical, cylindrical and bowl-like particles in sedimentation equilibrium gives information about the microstructures and Young's elastic modulus (0.1-16 Pa) of the colloidal crystals. (2) The microstructures of crystal-like macroions are clarified by reflection and transmitted-light spectrum measurements. Stability of the face-centered cubic and body-centered cubic lattice structures is studied as a function of macroion and foreign salt-concentrations, temperature, electric field, hydrodynamic pressure, shear rate, etc. The interparticle distances correspond to the effective sizes of macroions which include the Debye-screening length. (3) The structural relaxation times, translational-and rotational- diffusion constants of spherical and ellipsoidal colloids are discussed in gas-like, liquid-like and crystal-like solutions. These dynamical properties are reasonably explained by the Einstein-Stokes and Perrin theories, if we take account of the contribution of the Debye length. (4) Evidence of the important role of the Debye length is obtained from the unusual concentration dependencies of viscosity for deionized colloids: reduced viscosities of liquid-like colloids are much higher than would be expected by Einstein's prediction and decrease sharply with concentration. Furthermore, a sharp peak is observed in the reduced viscosity vs. concentration curves, which corresponds to the transition between liquid-like and crystal-like structures. All these properties of charged colloidal suspensions are adequately described by the electrostatic intermacroion repulsion and the simple idea of the elongated Debye-screening length around macroions.