REFRACTOMETRIC STUDIES OF LIQUID-LIKE AND CRYSTAL-LIKE COLLOIDS IN DEIONIZED SOLUTION

Refractive indices of colloidal spheres, i.e., colloidal silica spheres (8 nm in diameter) and monodisperse polystyrene latices (85 nm in diameter), are measured in deionized ("salt-free") solutions and in the presence of a small amount of NaCl. The reduced refractive index increments (refractive index increment divided by concentration) of "liquid-like" solution of deionized silica are higher than those in the presence of NaCl. A sharp peak is observed in the reduced refractive index increment vs concentration curves of the deionized polystyrene spheres. The peak corresponds to the transition between "liquid-like" and "crystal-like" structures. Electrostatic intersphere repulsion and the elongated Debye-screening length around the colloidal spheres are essential to explain the extraordinary properties. © 1990.