Copper-assisted weak polyelectrolyte multilayer formation on microspheres and subsequent film crosslinking

The formation of weak polyelectrolyte films on planar and spherical supports has recently evoked major interest, as such coatings allow novel material properties to be tunable by pH and salt adjustment of the polyelectrolyte deposition conditions. We report on the build up of multilayers of the weak polyelectrolytes poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) on submicrometer-sized polystyrene (PS) and silica colloid spheres (similar to500 nm) with the aid of copper ion templating. The copper ions complex to the carboxylate groups of PAA, facilitating the formation of PAA/PAH multilayers on the particles. Regular growth of the layers on the colloid spheres with each polyelectrolyte deposition step was confirmed by microelectrophoresis, single-particle light scattering (SPLS), and transmission electron microscopy (TEM), with an average bilayer thickness of similar to3 nm. The polyelectrolyte multilayer-coated particles formed stable colloidal dispersions, with zeta-potentials ranging from 30 mV (PAH outer layer) and -50 mV (PAA outer layer). Complementary quartz-crystal microbalance and UV-vis spectrophotometry studies on PAA/PAH multilayers formed on planar supports were performed to examine the film formation and the role of copper ion binding to the layers. PAA/PAH multilayers formed on colloid particles were also chemically crosslinked by using the activator 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC). The degree of film crosslinking could be readily controlled by varying the concentration of EDC employed. Following solvent decomposition of the template particles coated with crosslinked PAA/PAH multilayers, intact hollow polymer capsules were obtained. These capsules were found to be impenetrable to polystyrene.