Surface priming and the self-assembly of hydrogen-bonded multilayer capsules and films

We present a systematic study of how growth of hydrogen-bonded multilayers is affected by the substrate shape and charge as well as by the deposition conditions of a polycation precursor layer. We contrast growth of strongly bound poly(N-vinylpyrrolidone)/poly(methacrylic acid) (PVPON/PMAA) and weakly bound poly(ethylene oxide))/poly(methacrylic acid) (PEO/PMAA) systems when these multilayers are deposited onto bare or poly(ethylene imine) (PEI)-treated surfaces of CdCO3 crystals, colloidal silica particles, or silicon wafers. As compared to flat substrates, growth of hydrogen-bonded multilayers was significantly inhibited when colloidal particles were used as a substrate, presumably due to the enhanced chain removal by shaking the particulate substrate during the polymer adsorption. While in the PVPON/PMAA system robust multilayer deposition occurred on the precursor-treated substrate regardless of the adsorption history of the precursor layer, growth of PEO/PAMA films was critically dependent on the conditions of PEI adsorption. PEO/PMAA films could be grown on CdCO3 substrates when the PEI precursor was allowed to adsorb at a pH value higher than that used for hydrogen-bonding deposition, but PEO/PMAA film growth was inhibited when PEI was deposited at the same pH used for film deposition. We rationalize this effect in terms of the role the precursor layer plays on the growth of hydrogen-bonded multilayers, and we confirm our hypothesis by monitoring electrophoretic mobility, ionization, and the amount of polymer deposited within the precursor layer. Finally, we suggest two ways to facilitate growth of hydrogen-bonded multilayers onto substrates which carry unfavorably high negative charge: construction of hybrid hydrogen-bonded multilayers and the use of divalent cations as promoters of PMAA binding.