POLYELECTROLYTE ADSORPTION AT THE SOLID LIQUID INTERFACE - INTERACTION FORCES AND STABILITY/

The forces between negatively charged surfaces in the presence of an a dsorbing cationic copolymer of acrylamide and 2(methacryloyloxy) ethyl trimethylammonium chloride have been investigated using an atomic forc e microscope. The results were compared with measurements from adsorpt ion isotherm, electrophoretic mobility, stability, and light scatterin g experiments. The adsorbed amount of polyelectrolyte and adsorbed lay er conformation at the solid/liquid interface were found to be strongl y dependent on the polymer concentration from which initial adsorption takes place. At low polyelectrolyte concentrations unstable silica su spensions were observed from stability tests; light scattering experim ents indicate a large aggregate size under equivalent conditions. The adsorbed amount was also seen to be low, well less than monolayer cove rage, and force measurements indicated that the polymer was adsorbed i n a flat conformation. At high polyelectrolyte concentrations, an incr ease in the adsorbed amount was observed which resulted in a higher su rface coverage, a higher mobility and a stable suspension. Direct forc e measurements indicated the presence of an electrosteric barrier. (C) 1998 Elsevier Science B.V. Al rights reserved.