Forces between colloidal droplets in the presence of a weak polyelectrolyte

In this paper, we present the results on the forces between individual coll oidal liquid droplets in the presence of a weak polyelectrolyte, poly(acryl ic acid), using magnetic chaining technique. The effect of the repulsive fo rces have been investigated under different experimental conditions such as polyelectrolyte concentration, adsorption time, salt concentration etc. At a. PAA concentration of 0.01% (weight), a long range repulsive force profi le is observed due ta the adsorption of polyelectrolyte on the droplet, wit hout any irreversible aggregates even at very small inter-droplet spacing. Above a concentration of 0.01 wt% of PAA, formation of irreversible chainin g of droplets is observed at short inter-droplet separations due to polyele ctrolyte bridging. The onset of binding is also independently confirmed by microscopic observation, Compared to the slow adsorption on mica surfaces, the PAA adsorption on the colloidal droplets is found to be rapid. Up to 0. 1 M NaCl, the range of repulsion and the hydrodynamic radius of the droplet is found to be increasing.