Stability of copper phthalocyanine dispersions in organic media

This paper deals with the stability of dilute dispersions of copper phthalo cyanine in organic solvents, a subject of importance to the paint and ink i ndustries. It has been found that quite small surface potentials (a few mil livolts) are sufficient to stabilize the dilute dispersions of the particle s in solvents of low dielectric constant (possibly because this would be a constant charge system) though insufficient to stabilize particles in solve nts with dielectric constants above about 20. Addition of organic acids enh anced the particles' stability, probably by a proton-exchange mechanism, an d addition of an organic-soluble electrolyte, tetrabutylammonium bromide, c aused all systems to flocculate. The presence of a polymer at concentration s above about 1% caused flocculation to occur, probably by a depletion mech anism. The attractive depletion energy increased with polymer concentration , resulting in the sedimentation volume increasing with polymer concentrati on.