Interfacial behaviour of binary polymer mixturesI. Effect of uncharged polymers and of their mixtures on the stability of silver iodide sol

Abstract

The adsorption from aqueous solutions of methylcellulose (MC), polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), adsorption of their binary mixtures on silver iodide sol, and the effect of these polymers and polymer mixtures on the stability of silver iodide sol, have been studied. All these polymers show high affinity-type adsorption isotherms and the adsorption is only partially reversible upon dilution. The order of preferential adsorption for the polymers is as follows; PVP &>; PVA &>; MC. The weakly adsorbed polymers, at high surface coverage, can be displaced from the interface by the preferentially adsorbed polymers. Synergism has been found in the flocculating effect of the MC—PVP and the PVA—PVP mixtures. At the onset of the stabilizing region, some increase in the effectiveness of the above two mixtures has also been observed. Non-additivity can be observed when the difference in the segment affinity of the two polymers for the particle surfaces is high enough. When synergism occurs, the conformation of the weakly adsorbed polymer appears to be distorted at the solid/liquid interface by the preferentially absorbed polymer. This “irregularly” extended polymer conformation is especially favourable for bridging flocculation.