Coagulation kinetics and the stability of surfactant-free emulsion-polymerised latexes

Abstract The stability factor of styrene/sulfopropyl methacrylate (styrene/SPM) and styrene/3-[ N , N -dimethyl- N -(methacryloxyethyl)ammonium]propane sulfate (styrene/ SPE) latexes was studied using the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and the critical coagulation concentration, CCC, was deduced for the latexes. Photon correlation spectroscopy was used to study ionic stabilities. The stability factor was determined as the ratio of the rate constant for rapid coagulation to that of slow coagulation, obtained from the coagulation kinetics data. The log-log plot of the stability factor, W , as a function of NaCl electrolyte concentration shows an asymptotic decrease in W of both latexes. DLVO theory was successfully employed, whereby the characteristic properties of the diffuse electric double layers or the Stern layers around latex particles in terms of their Hamaker constants and diffuse potentials were determined. The electric double layer thickness decreases with increasing NaCl concentration. Stability curves revealed a higher CCC value for the styrene/SPM latex than for the styrene/SPE latex, which is in accordance with the higher surface charge density and an indication of a better stability.