LAUSR

Abstract 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 μ and the interface ion polarizability γ are used as criteria for the effective charge of CMC-alumina particles. The light scattering intensity I0 and the field-strength dependence τ(E2) of the relaxation time τ are used as criteria for aggregation. The polymer-concentration dependences μ(CCMC), γ(CCMC) and I0(CCMC) under and above the recharging point are measured at different degrees of proton dissociation α and fraction φ of counterions condensed on the adsorbed polyelectrolyte chains: α ≈ 1/2, φ = 0 at pH 4.5, and α ≈ 1, φ ≈ 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.