Effect of electrolyte type on the electrokinetic behavior of carboxylated polystyrene model colloids

Carboxylated polystyrene latex particles were prepared by emulsifier-free emulsion polymerization of styrene using an azo-initiator (ACPA), which provides carboxyl end groups on the latex surface. Two latexes were characterized using TEM, PCS, conductimetric and potentiometric titrations, and electrophoretic mobility. To determine the hydrophobic or hydrophilic character of these latexes, the maximum adsorption of a non-ionic surfactant (Triton X-100) was also studied and compared with other type of latexes. The electrophoretic mobility of these functionalized model colloids was studied in the presence of various types of inorganic electrolytes. The mu(e)-log C curves of these latexes exhibit a smooth maximum at an electrolyte concentration of around 10(-3) and 5.10(-3) M for 1:1, 2:1 and 1:2 electrolytes. When a 3.1 electrolyte (LaCl3) was used, the electrophoretic mobility changed to positive values at high concentration due to the specific adsorption of lanthanum species. In general, the surface characteristics of these carboxylated latexes are very different in comparison to other latexes with the same functionality because the carboxyl groups are provided by the initiator, while in most of the cases these groups are provided by ionic comonomers (acrylic, methacrylic acids, etc.) used in the copolymerization with styrene.