Electroacoustic characterization of electrokinetics in concentrated pigment dispersions: 3-Cyano-4-(4′-butanesulfonamidophenyl)-5-furylidene-furan-2-one

The surface and colloid chemistry of organic pigment dispersions have largely been ignored in the literature, although organic pigments play a crucial role in classical and ink jet printing and imaging. This paper presents detailed measurements of an aqueous dispersion of the title compound, prepared without added surfactant, and examines the adsorption of various anionic surfactants via electrokinetic sonic amplitude (ESA) measurements. Quantitative adsorption data are compared with adsorption isotherms obtained via phase separation methods and are found to be in good agreement. Determination of saturation monolayer adsorption is significantly faster and more convenient using ESA measurement technology. However, some of the surfactants examined exhibited multilayer or partial multilayer adsorption. A surfactant modeled after the title compound was synthesized and exhibited particularly effective stabilization, although the adsorption appears slightly weaker than the classical surfactants studied. The intrinsic negative surface charge observed in aqueous dispersion of the title compound was identified as due to mechanicochemical activation of surface molecules to hydrolyze the furanone ring to the α-cyano maleic acid moiety. Electrophoretic mobility measurements as a function of volume fraction at various ionic strengths indicate that increasing electrophoretic mobility magnitudes accompanying increasing NaCl concentrations were due to preferential adsorption of chloride to the particle surfaces.