Charging and aggregation of negatively charged colloidal latex particles in the presence of multivalent oligoamine cations

Charging and aggregation of negatively charged carboxyl latex particles in the presence of positively charged linear oligoamines containing 1-6 amine groups were investigated by electrophoretic mobility and dynamic light scattering. The oligoamines of low valence resemble simple inert salts and destabilize the suspensions by screening their charge. The oligoamines of higher valence induce overcharging at low concentrations, whereby destabilization is triggered by charge neutralization. At higher concentrations, destabilization is also induced by screening. The onset of first fast aggregation regime scales with the inverse six power of the valence in agreement with the Schulze-Hardy rule. Aggregation rates can be relatively well described by the DLVO theory which indicates that interactions are governed by van der Waals and electrostatic double layer forces. (c) 2012 Elsevier Inc. All rights reserved.