Stability of aqueous suspensions of alumina particles with adsorbed (carboxymethyl)cellulose

The influence of the counterion condensation on the colloid stability of alumina suspension with added carboxymethylcellulose (CMC) is investigated by electric light scattering and microelectrophoresis. The electrophoretic mobility mu and the interface ion polarizability gamma are used as criteria for the effective charge of CMC-alumina particles. The light scattering intensity I-0 and the field-strength dependence tau(E-2) of the relaxation time t are used as criteria for aggregation. The polymer-concentration dependences mu(C-CMC), gamma(C-CMC) and I-0(C-CMC) under and above the recharging point are measured at different degrees of proton dissociation a and fraction f of counterions condensed on the adsorbed polyelectrolyte chains: alpha approximate to 1/ 2, phi= 0 at pH 4.5, and alpha approximate to 1, phi approximate to 1/3 at pH 6.0. The results show out that the colloid stability is conditioned by the effective charge of CMC-alumina particles determined by the surface charge, the dissociated carboxylic groups of CMC chains and the condensed counterions. The particle aggregation about the recharging point (at 1: 50 CMC/alumina) is explained with hetero-coagulation by polyelectrolyte chain bridging conditioned by the reduced total charge, surface charge-patches, low surface occupation and the high rigidity of CMC chains.