COLLOIDAL FORCE MEASUREMENTS IN THE PRESENCE OF A POLYELECTROLYTE

We report investigations of the repulsive forces between monodispersed ferrofluid droplets in the presence of a weak polyelectrolyte, poly(a crylic acid) (PAA), using a magnetic chaining technique. Two interesti ng observations were made during our investigations. At a PAA concentr ation of 0.01 wt%, a long-range repulsive force profile was observed d ue to the adsorption of polyelectrolyte onto the droplet, without any irreversible aggregates even at very small inter-droplet spacings. Abo ve a concentration of 0.01 wt% of PAA, formation of irreversible chain ing of droplets was observed at short inter-droplet separations due to polyelectrolyte binding or bridging. The onset of binding was also in dependently confirmed by microscopic observation.