Salt effects on the structural tailoring of layer-by-layer assembled polyelectrolyte complexes and salt-containing polyelectrolyte films

Structural tailoring of layer-by-layer (LbL) assembled polymeric films prepared by alternate deposition of polyelectrolyte-polyelectrolyte complexes (PECs) and oppositely charged salt-containing polyelectrolyte was systematically studied as a function of NaCl concentration in the polyelectrolyte solution. At pH 9.3, positively charged poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) complexes (denoted as PAH-PAA9.3) could be LbL assembled with poly(sodium 4-styrenesulfonate) (PSS) to produce PSS/PAH-PAA9.3 films even with high NaCl concentration in PSS solution. Moreover, both the thickness and structure of the films were strongly depended on the concentration of NaCl in PSS solution. The salt in PSS solution can influence the conformation of PSS chains, but cannot interfere with the interaction and structure of PAH-PAA complexes deposited on substrates. Therefore, at relatively high NaCl concentration, a rough surface with hierarchical micro- and nanostructures can be obtained due to the coiled conformation and increased rigidness of PSS when they were LbL deposited with PAH-PAA complexes. By contrast, LbL deposition of flexible and extended PSS with PAH-PAA complexes at low NaCl concentration can produce a thin film with smooth structure. The present study is meaningful in deeply understanding the salt effect on the deposition behavior and structural tailoring of LbL assembled PECs and salt-containing polyelectrolyte films.