Role of sequential adsorption of polymer/surfactant mixtures and their conformation in dispersion/flocculation of alumina

The role of sequential adsorption of a non-interacting pair of polymer (pol yacrylic acidPAA) and surfactant (sodium dodecyl sulfate-SDS) on alumina pa rticles and in determining the stability of their suspensions was studied w ith particular attention to the conformation of the polymer. It was found t hat the sequence of addition is of critical importance in determining the d ispersion/flocculation of this system. When SDS was added first, both PAA c onformation and suspension stability varied with SDS concentration. Whereas when PAA was added first, the subsequent adsorption of SDS molecules had n o effect on either the polymer conformation or the suspension stability. Th is is attributed to masking of SDS species by the larger polymer chains. SD S can not however be completely masked by PAA chains once the PAA concentra tion is decreased below the optimal concentration for flocculation. When th e stirring duration was increased, the mode of addition showed no effect su ggesting that the system then reaches equilibrium. Interestingly, a small a mount of pre-adsorbed PAA was found to facilitate the adsorption of SDS. (C ) 1999 Elsevier Science B.V. All rights reserved.