Polyelectrolyte adsorption at the solid/liquid interface interaction forces and stability

The forces between negatively charged surfaces in the presence of an adsorbing cationic copolymer of acrylamide and 2(methacryloyloxy)ethyltrimethylammonium chloride have been investigated using an atomic force microscope. The results were compared with measurements from adsorption isotherm, electrophoretic mobility, stability, and light scattering experiments. The adsorbed amount of polyelectrolyte and adsorbed layer conformation at the solid/liquid interface were found to be strongly dependent on the polymer concentration from which initial adsorption takes place. At low polyelectrolyte concentrations unstable silica suspensions were observed from stability tests; light scattering experiments indicate a large aggregate size under equivalent conditions. The adsorbed amount was also seen to be low, well less than monolayer coverage, and force measurements indicated that the polymer was adsorbed in a fiat conformation. At high polyelectrolyte concentrations, an increase in the adsorbed amount was observed which resulted in a higher surface coverage, a higher mobility and a stable suspension. Direct force measurements indicated the presence of an electrosteric barrier.