CHARACTERIZATION OF HAIRY LATEX-PARTICLES WITH COLLOIDAL PARTICLE SCATTERING

Many experiments in the literature suggest that the surfaces of colloi dal latex particles suspended in water are not smooth. The surface rou ghness is often referred to as being ''hairy''. We determined the thic kness of the hairy layer on two 5 mu m latex particles by colloidal pa rticle scattering, a new method recently developed by us to measure su rface forces. The results are consistent with electrophoretic mobility measurements. The thickness can be determined with an error of 1 nm. Besides the layer thickness, qualitative information about the evennes s of the hairy layer can also be obtained. According to our calculatio ns, the stabilizing mechanism under our experimental conditions is rel ated to the hairy layer but cannot be ascribed to steric repulsion. In stead, a layer of immobilized water in the hairy layer effectively low ers the van der Waals interactions, thus increasing the relative impor tance of electrostatic repulsion. Hamaker constant measurements on the same latex samples indicate that there is no hydrophobic force acting between latex surfaces at separations larger than 28 nm.