Adsorption of Anions on the Surface of Charge-Free Latex Particles as Revealed by Turbidimetric Measurements

The preferential adsorption of anions on the surface of latex particles without permanent charges is investigated. The latex consists of particles of 83 nm diameter stabilized by a thin layer (1.3 nm) of polyethylene oxide chains. The serum of the latex is adjusted to an ionic strength of 0.001 by adding different salts (KCl, KI, LiF, LiI, NaI). The structure of the latex particles has been studied by small-angle X-ray scattering and by dynamic light scattering whereas the interaction of the particles was investigated by turbidimetry. The latter method gives clear indication that the particles repel each other due to the electrostatic repulsion. The effect is much more pronounced in the presence of I- anions than in the presence of Cl- or F-. Since all other mechanisms of long-range repulsive interactions can be ruled out, the results presented herein demonstrate the preferential adsorption of anions, in particular of I- onto the latex surface. Copyright 1998 Academic Press.