The role of polymer conformation in colloidal stability

In this investigation the conformational characteristics of polyacrylic acid in bulk and in adsorbed state were studied along with various suspension stability properties, polymer adsorption behavior and the zeta potential of the particles in order to delineate the mechanism by which polymer conformation affects colloidal stability and to develop methods for better control of colloidal systems.; It was found that settled solids, sediment volume and suspension permeability were enhanced by polyacrylic acid adsorbed in stretched conformation. Increased supernatant clarity, on the other hand, was achieved with polyacrylic acid in coiled conformation, i.e., under conditions of minimum zeta potential. Under the coiled-transformed to-stretched conformations, achieved through pH shift from 4 to 10, flocculation was drastically enhanced at lower polymer concentration; while flocculation and then a stable dispersion were observed at higher polymer concentrations. Differences in the dispersion/flocculation behavior is explained on the basis of concentration-dependent conformational changes and zeta potential. Polyacrylic acid initially adsorbed in stretched conformation did not coil or desorb with pH shifting from 10 to 4. Alumina stability did not exhibit the same trend as the polyacrylic acid conformation. Flocculation was depressed at low polyacrylic acid concentration, while a maximum in flocculation was observed at higher polymer dosage in the alkaline region. This flocculation behavior was attributed to the changes in the orientation of the adsorbed polymer from dangling to flat and the surface charge of the alumina particles.; Polyacrylic acid conformation has shown a strong dependency on the type and concentration of dissolved mineral species. Complexation of carboxylic pendant groups with dissolved cationic alumina species was observed to cause polyacrylic acid to assume a compact coiled structure, resulting in improvement in alumina flocculation, relative to that of alumina-free polyacrylic acid system, especially at high polymer dosage. Polyacrylic acid conformation was also found to be dependent on the presence of polydimethylallylammonium chloride (DMDAAC). When DMDAAC is added to polyacrylic acid-coated alumina particles, DMDAAC complexed and bridged with one or more polyacrylic acid species, causing the latter to become less stretched. These changes in polyacrylic acid conformation significantly promoted the inter-particle approach and consequently enhanced flocculation. (Abstract shortened with permission of author.)...