Dispersion of aqueous nano-sized alumina suspensions using cationic polyelectrolyte

In this paper, we investigate and report the effects of a cationic polyelectrolyte, polydiallydimethylammonium chloride (PDADMAC), on the stability of nano-sized alumina (α-Al₂O₃) suspension. Due to the static electrical repulsion interactions, PDADMAC show significant adsorption on α-Al₂O₃ only at alkaline pH. Considerable amount of non-adsorbed free PDADMAC exist in α-Al₂O₃ suspensions dispersed by PDADMAC at acidic and neutral pH. At 1.0 wt.% PDADMAC addition, α-Al₂O₃ became highly positively charged (>50 mV) in the entire pH range contrast with that the stability of α-Al₂O₃ suspension is enhanced only over the basic pH range in the presence of anionic polyelectrolyte. Free PDADMAC electrolyte in suspension results in increasing viscosity of α-Al₂O₃ suspensions dispersed with PDADMAC at alkaline and neutral pH. However, non-adsorbed free PDADMAC in suspension do not contribute to viscosity increase in acidic α-Al₂O₃ suspensions and α-Al₂O₃ suspensions dispersed with PDADMAC show the best flow behavior at acidic pH.