Surface characterization of soap-free carboxylated polymer latices

Abstract

The surface characteristics of carboxylated polymer latices舒styrene/acrylic acid copolymer (PS/PAA) and styrene/methacrylic acid copolymer (PS/PMAA)舒 were investigated. Polystyrene (PS) latex was used as a reference sample. These latices were prepared in a soap-free system, using potassium persulfate as the initiator. Conductometric titration curves of PS and carboxylated latices showed both strong and weak acid groups to exist on the surface of latex particles. The surface charge density (ॣ) for PS/PAA latex was proportional to the amount of acrylic acid (AA) used in the copolymerization (thus, ॣ- for PS/PAA5 latex was larger than that for PS/PAA2 latex; the subscripts 5 and 2 represent the mol% of AA monomers used in the copolymerization). However, ॣ for PS/PMAA5 latex was smaller than that for PS/PAA5 latex, although the mol% of acid monomers used in the copolymerization was the same for both latices. ॣ for carboxylated latices increased with increasing pH, but the pH dependence of ॣ for PS latex was not very pronounced. The ॐ-pH curves for these latices were considerably different from the ॣ-pH curves. This is probably because the Stern potential and the position of the shear plane in the electrical double layer differ between the two latices. Methylene Blue adsorption onto PS and PS/PAA latices was measured as a function of pH. The overall tendency of the dye adsorption was more similar to the ॣ-pH curves than the ॐ-pH curves. © 1984 The Society of Polymer Science, Japan.