Layer-by-layer (LbL) assemblies of oppositely charged polyelectrolytes exhibit a physical response to changes in the post-assembly ionic environment that can lead to swelling or contraction of the thin film. This response depends on both the type and concentration of the counterion solution to which the thin film is exposed. Although this phenomena has been studied quite extensively, relatively few studies have been conducted in which this responsive behavior is monitored in real time. In this study, the post-assembly effect of counterion type and concentration on the physical conformation and internal composition is explored for poly(diallyldimethylammonium chloride) –poly(styrenesulfonate) (PDAC/PSS) LbL thin films formed in the presence of NaCl. The salts studied include KBr, NaBr, and KCl. Quartz-crystal microbalance with dissipation is employed to monitor the physical response behavior of the LbL thin films upon exposure to various monovalent counterion species and combinations, and comparison among the different ion types is discussed. In some cases, swelling up to 100% and -15% (contraction) was observed in the limit of high and low salt concentration, respectively. Neutron activation analysis (NAA) also reveals that the internal composition of PDAC/PSS LbL films changes dramatically during the ion exchange process with little dependence on concentration of the exchange counterion species. These results generally reveal the relationship between salt type and salt concentration with changes in multilayer structure.

Swelling behavior of polyelectrolyte multilayers in the presence of various monovalent ions

254th National Meeting (2017)

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