Abstract
The desorption of polyelectrolyte molecules adsorbed on barium sulphate in the presence of various displacing species is reported. When polyacrylate (PAA) was both the adsorbed and displacing species, no significant desorption occurred when the dispersion medium was water. However, significant desorption occurred in 0.1 mol dm −3 NaCl, but only when the displacing PAA had a higher molecular mass than that adsorbed. The simultaneous adsorption of PAA and polystyrene sulphonate (PSS) is also reported as a function of the molecular mass of the two species and at different relative concentrations. The adsorption of PAA decreased with increase in the ratio of the weight of barium sulphate to the volume of polymer solution ( W/V), whilst that of PSS increased. In H 2O there was a critical W/V ratio below which there was no detectable adsorption of PSS. The amount of PSS excluded from the surface increased as the ratio of PAA to PSS concentrations increased. The results indicate that the diffusion rate of PAA is the dominating factor in determining the surface composition. This suggests that the PSS must require a significant time from first contact of the molecule to complete adsorption, and in this time, newly arriving PAA molecules displace the PSS.
Published Version
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