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 (polyacrylic acidPAA) and surfactant (sodium dodecyl sulfate-SOS) on alumina particles and in determining the stability of their suspensions was studied with particular attention to the confonnation of the polymer. It was found that the sequence of addition is of critical importance in detennining the dispersion/flocculation of this system. When SOS was added first. both P AA conformation and suspension stability varied with SOS concentration. Whereas when PAA was added first, the subsequent adsorption of SOS molecules had no effect on either the polymer conformation or the suspension stability. This is attributed to masking of SOS species by the larger polymer chains. SOS can not however be completely masked by PAA chains once the PAA concentration is decreased below the optimal concentration fOT flocculation. When the stirring duration was increased, the mode of addition showed no effect suggestjng that the system then reaches equilibrium. Interestingly, a small amount of pre-adsorbed PAA was found to facilitate the adsorption of SOS. e 1999 Elsevier Science B.V. All rights reserved. x..,words: Sequential adsorption; POlymer/surfactaDt mixtures; Dispersion/floa:ulatioo; Alumina little work on co-adsorption of non-interacting polymers and surfactants. In one of the rare examples of the latter, Gebhardt and Fuerstenau [I), while confirming the absence of any interaction between polyacrylic amide (PAAm) and sodium dodecyl sulfonate (SDSO3) in solution, demonstrated that pre-adsorbed P AAm on hematite had no effect on either the adsorption of SDSO3 (except at high concentrations of the latter) or on its electrophoretic mobility. On the other hand, Hollander [2) determined that each ingredient in a I ntToductjon Since both polymers and surfactants adsorb on solids in certain operations, it is useful to determine the effect each has on the adsorption properties of the other. Most studies in the past have focused on systems where there are interactions between the polymer and the surfactant with very . Corresponding aulhor. Tel.: + 1-212-8542926; fax: + 1 212-8548362; e-rnaiJ: [email protected]. 0927-77S7{99/S see front matter