Atomic force microscope characterization of PAH/PAZO multilayers

The buildup of a poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzene sulfonamido]-1,2-ethanediyl, sodium salt] (PAZO) layer adsorbed onto a already adsorbed layer of poly(allylamine hydrochloride) (PAH) was shown to be ruled by two processes, a nucleation process which occurs for short adsorption times and a process having longer characteristic times. During the nucleation process the adsorbed amount is seen to increase very rapidly and is dependent of PAZO concentration. The adsorbed PAZO molecules create a potential barrier that to make difficult that more molecules are adsorbed. However the presence of cations in the solution accounts for adsorption the continuation of adsorption in a second process, as they tend to be adsorbed lowering the potential barrier and allowing more PAZO molecules to be adsorbed. These processes are shown to be consistent with surface morphology evolution, it was observed an increase of roughness for short adsorption periods of time and a subsequent decrease of the surface roughness for longer adsorption times.