Polyelectrolyte adsorption processes characterized in situ using the quartz crystal microbalance technique: alternate adsorption properties in ultrathin polymer films

The alternate adsorption processes of polyelectrolytes from solution have been investigated in situ using a functionalized (gold electrode) quartz substrate via the quartz crystal microbalance (QCM) technique. The deposition process involved the alternate layer by layer electrostatic (Coulombic) interaction between oppositely charged adsorbing polyelectrolytes resulting in ultrathin multilayer films. Three kinds of polyelectrolyte combinations were used: poly(diallyldimethylammonium chloride) (PDADMAC), poly(ethylenimine) (PEI) and poly(allylamine hydrochloride) (PAH) as the cationic polymers and poly(sodium-4-styrensulfonate) (PSS) as the anionic polymer for polycation/polyanion combinations. The electrical behavior of the piezoelectric ‘quartz crystal’ was sensitive to the adsorption properties of the polyelectrolytes, thus allowing close observation of the time-dependent adsorption processes. The adsorption relationship was explored for different polyelectrolyte pair-combinations, alternate solution concentration and the presence of rinsing and drying steps. The results showed that the amount of frequency change is mostly dependent on the immediate subphase environment of the crystal surface, i.e. aqueous environment versus air in relation to the classic Sauerbrey equation.