Electrophoretic mobility of latex particles: effect of particle size and surface structure

The influence of particle size on the electrophoretic mobility of negativel y charged latex particles was examined by a comparison between theory and e xperiment. Theoretical values for the dependence of the mobility on electro lyte concentration were calculated by a modified White-O'Brian model (Hidal go-Alvarez et al., Adv. Coll. Interf. Sci. 67 (1996) 1) which enables the c onsistent calculation of the zeta (zeta) potential. For three polystyrene l atexes of different size but similar surface charge density the measured mo bilities increased with increasing radius for the electrolyte range under c onsideration. The theoretical calcalations resulted in a qualitatively corr ect prediction of the experimental data. The experimental comparison of the mobilities of hydrophobic and hydrophilic particles of similar size and su rface charge density lead to the conclusion that hydrophilic surfaces lower the electrophoretic mobility. The same theoretical model was able to descr ibe correctly this observed behavior by assuming a greater distance of the plane of shear. The effect of a spatial distribution of the charges was exa mined by characterizing an electrosterically stabilized latex. Contrary to all standard latices with surface charges this latex didn't show any mobili ty maximum as a function of electrolyte concentration. (C) 1999 Elsevier Sc ience B.V. All rights reserved.