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Positively charged poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) complexes (noted as PAH-PAA) with a molar excess of PAH were layer-by-layer (LbL) assembled with polyanion poly(sodium 4-styrenesulfonate) (PSS) to produce multilayer films. The film structure and deposition behavior of the PAH-PAA/PSS films were influenced by the structure of PAH-PAA complexes in solution. For the PAH-PAA complexes with a low ratio of PAA to PAH the PAH-PAA complexes have low-level cross-linking and are flexible. The resultant PAH-PAA/PSS films have a thin film thickness and smooth surface and exhibit a nonlinear deposition behavior where the amount of PAH-PAA complexes and PSS deposited in each deposition cycle are larger than in its previous cycle. The PAH-PAA complexes with a high ratio of PAA to PAH have high-level cross-linking and are rigid. The PAH-PAA/PSS films constructed from the rigid PAH-PAA complexes have a large film thickness and rough surface and exhibit a linear deposition behavior. Deposition of the PAH-PAA/PSS films was well characterized by quartz crystal microbalance, atomic force microscopy, and scanning electron microscopy. The thermally cross-linked PAH-PAA/PSS films can be released from substrate to form stable free-standing films by an ion-triggered exfoliation method. Meanwhile, positively charged PAH-PAA complexes can be LbL assembled with negatively charged PAH-PAA complexes with a molar excess of PAA to produce multilayer films. Use of polyelectrolyte-polyelectrolyte complexes as building blocks for LbL fabrication provides a facile way to tailor the structures of the resultant films by simply changing the structure of the complexes in solution.

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Noncharged pyrene molecules were incorporated into multilayer films by first loading pyrene into poly(acrylic acid) (PAA)-stabilized cetyltrimethylammonium bromide (CTAB) micelles (noted as PAA&(Py@CTAB)) and then layer-by-layer (LbL) assembled with poly(diallyldimethylammonium chloride) (PDDA). The stable incorporation of pyrene into multilayer films was confirmed by quartz crystal microbalance (QCM) measurements and UV-vis absorption spectroscopy. The resultant PAA&(Py@CTAB)/PDDA multilayer films show an exponential growth behavior because of the increased surface roughness with increasing number of film deposition cycles. The present study will open a general and cost-effective avenue for the incorporation of noncharged species, such as organic molecules, nanoparticles, and so forth, into LbL-assembled multilayer films by using polyelectrolyte-stabilized surfactant micelles as carriers.

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