AFM studies of amine surfactant hemimicelle structures at the mica-water interface

The adsorption of cationic surfactants with primary, secondary, tertiary and quaternary ammonium bromide head-groups attached to a single dodecyl hydrocarbon chain onto the muscovite mica basal plane has been investigated using both a flat plate streaming potential apparatus and by atomic force microscopy. The analysis of images of the adsorbed surfactant layer shows the presence of aggregate structures of variable size. The size of these aggregate patches was compared at C₀ (the point of charge reversal) for all four molecules. The data were found to be consistent with the extent of two-dimensional aggregation being the predominant driving force for adsorption.