Polyelectrolyte multilayers were constructed from poly(styrenesulfonate), PSS, and poly(diallyldimethylammonium) with regularly interspersed layers of deuterated PSS. Annealing, by salt, of the fuzzy internal layering within this multilayer was followed using neutron reflectometry. A “limited source” diffusion model fit the data well and showed that polyelectrolyte migrates much more slowly within the bulk of a multilayer than at the surface. Enhanced surface mobility and a nonlinear increase in diffusion rate with salt concentration were explained by a salt doping model, where correlated short lengths of polyelectrolyte move by exchange with counterions (“extrinsic charge”) doped into the ultrathin film of polyelectrolyte complex on exposure to solutions of high ionic strength.

Self-exchange of isotopically labeled polycarboxylic acid within a polyelectrolyte multilayer proceeds to completion and is reversible. Similar exchange with poly(styrene sulfonate), which forms nonlabile polyelectrolyte complexes, is slow and irreversible but is facilitated by polyvalent ion pairing interventions of a third polyelectrolyte. This is an example of accelerated kinetics in "sticky" synthetic systems associated by nonspecific polyvalent interactions.

Homopolynucleotides--poly(adenylic acid), poly(A), and poly(uridylic acid), poly(U)--were assembled, layer-by-layer, into thin films with poly(ethylenimine), PEI. Various combinations and sequences of polynucleotide and PEI were used to highlight contributions of electrostatic versus hydrogen bonding as driving forces for multilayer build-up. Assembly of alternating poly(A) and poly(U) failed to yield growing films, due to excessively strong interactions between these complimentary strands. The surface morphology of multilayers depended on the deposition order and whether films had been annealed by salt. Films assembled from preformed A/U duplexes (having high persistence lengths) were very smooth. Individual adsorption steps, followed by optical waveguide light-mode spectroscopy, showed that only complementary polynucleotides adsorb by H-bonding to the surface of a growing multilayer. In contrast to behavior usually observed for polyelectrolyte multilayer build-up, the films decreased in thickness with increasing salt concentration.