POLYSTYRENE SULFONATE ADSORPTION AT WATER GRAPHON AND WATER AIR INTERFACES

The adsorption behaviour of a series of sodium polystyrene sulfonates with a narrow distribution of molecular weight was studied at the solid-liquid interface. Graphitized carbon black (graphon) was chosen as a model surface for real coal used in the preparation of coal-water slurries. Graphon has a highly homogeneous surface with virtually no polar groups and with a large specific area. Preliminary studies on the kinetics of adsorption were performed in order to establish attainment of steady-state conditions. The kinetic results were analyzed considering several models and the results were interpreted with a two-step process involving diffusion towards the interface and reorientation of the macromolecules at the surface. Adsorption at the graphon-water interface was found to follow the Langmuir equation for every sample with similar adsorption energies. The dependence of the maximum of adsorption on molecular weight was used to obtain information on the macromolecular conformation at the interface and, using a simplified fractal approach, on the graphon surface. Adsorption isotherms at the water-air interface were also recorded. The dependence of surface tension on polymer concentration and on polymer molecular weight was used to obtain information on the structure of the adsorbed layer and on the energetics of the process. The results obtained at the water-air interface were correlated to the polyelectrolyte behaviour at the liquid-solid interface.