Water Content and Buildup of Poly(diallyldimethylammonium chloride)/Poly(sodium 4-styrenesulfonate) and Poly(allylamine hydrochloride)/Poly(sodium 4-styrenesulfonate) Polyelectrolyte Multilayers Studied by an in Situ Combination of a Quartz Crystal Microbalance with Dissipation Monitoring and Spectroscopic Ellipsometry

The buildup of polyelectrolyte multilayers (PEMs), fabricated by the layer-by-layer (LBL) assembly, was followed in situ by the combination of a quartz crystal microbalance with dissipation monitoring (QCM-D) and spectroscopic ellipsometry in a single device. PEMs composed of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS) polyelectrolyte pairs and of poly-(diallyldimethyl ammonium chloride) (PDADMAC) and PSS were built up to 17 layers. The combination of ellipsometry and QCM-D allowed simultaneous determination of the acoustic mass, which comprises both the mass of the polymer and solvent, and the optical mass which corresponds to the polymer mass alone. From these parameters, the hydration of the PEM was calculated layer by layer. The linearly growing PAH/PSS PEMs showed a constant absolute content of water throughout the assembly, while the relative contribution of water to the PEM mass content approached zero, when grown in 0.5 M NaCl. Rinses with water between polyelectrolyte deposition steps resulted in a hydration of approximately 40%. The supralinearly growing PDADMAC/PSS PEMs exhibited a remarkable dependence of the hydration on the polyelectrolyte that was deposited last. Implications for the mechanism of assembly of the PEMs are discussed.