Since they were made popular more than two decades ago, thin films termed polyelectrolyte multilayers (PEMUs) have gained widespread attention for their potential uses as membranes, reservoirs and drug carriers, among others. Here, two core concepts, overcompensation and polymer kinetics, affecting the layer-by-layer buildup of PEMUs were elucidated in a series of radiolabeling and isotopic exchange experiments. Both polymers used in this study, poly(diallyldimethylammonium) and poly(styrenesulfonate), were found to reach approximately the same limit when added in excess to stoichiometric thin films. Their equilibrium overcompensation did not depend on salt concentration and polymer molecular weight. The diffusion of polymer chains and sites – the hopping of counterions between one monomeric site and another – was also examined, showing that the latter is orders of magnitude faster than the former. Buildup of multilayers was found to be mainly dominated by site diffusion, which explains their internal layered structure. A universal plot connecting salt concentration with the site diffusion coefficients of the polycation and the polyanion was established. It served as a starting point to inspect different multilayer buildup mechanisms using the same polyelectrolyte pair, and, in a broader sense, as a guide to the formation of these films and other forms of polyelectrolyte complexes.

Insights into the assembly of polyelectrolyte multilayers and complexes

255th National Meeting (2018)

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