Stable colloids at the isoelectric point: Dipolar vs. electrostatic interactions

AbstractHypothesis range stability of some colloid systems at the isoelectric point may be explained by interparticle electrostatic interactions (attractive and repulsive) of different electric charge patches on the particles’ surface, related to differences of their surface structure and possibly to adsorption of charged species on them. The coincidence of the minimum colloid stability with the electro-optically observed minimum of the particle electric polarizability (EP) is not in favor of attractive interparticle dipolar interactions playing a major role for the stability as stated before [1]. ments s dispersions of rod-like palygorskite particles + surfactant cetyl pyridinium chloride (CPC) were studied at different CPC concentrations by optic, electro-optic and microelectrophoretic methods. Thus the CPC concentration dependences of the stability, EP and ζ-potential were established. gs colloid stability at considerable ζ-potentials (about −30 mV) well below the isoelectric point was found in Ref. [1]. The CPC concentrations, at which the lowest stability was observed experimentally, corresponded well to that of a minimum value of the EP. The new hypothesis and interpretation for the major importance of electrostatic interactions are in good accord with the present day knowledge in Colloid Science for deviations from the Derjaguin–Landau–Verway–Overbeek (DLVO) theory of colloid stability.