Nonstoichiometric interpolyelectrolyte complexes (NIPECs) as colloidal dispersions formed by the interaction of synthetic polycations which possess ammonium quaternary centers attached to an acrylic macromolecular chain, derived from poly(N,N-dimethylaminoethyl methacrylate), or a natural polycation, chitosan, with poly(sodium-2-acrylamido-2-methylpropanesulfonate) (PAMPS), and three random copolymers of AMPS with tert-butylacrylamide or methyl methacrylate, were prepared. The effects of polyelectrolyte characteristics and concentration on the complex features were investigated by turbidimetric titration and dynamic light scattering, the molar ratio between the positive and negative charges ranging between 0.05 and 0.4. The nonstoichiometric complex nanoparticles were tested in the destabilization of kaolin model dispersion and proved to be more efficient than polycations alone, especially as concern the broadness of the flocculation window. The highest efficiency of the NIPECs dispersions was found when they have been prepared at very low molar ratios between charges (n(-)/n(+) < 0.1). (C) 2010 Elsevier B.V. All rights reserved.