title: Assembly of multilayer films from polyelectrolytes containing weak and strong acid moieties.
abstract: Multilayer films were assembled from a copolymer containing both weakly and strongly charged pendant groups, poly(4-styrenesulfonic acid-co-maleic acid) (PSSMA), deposited in alternation with poly(allylamine hydrochloride) (PAH). The strongly charged groups (styrene sulfonate, SS) are expected to form electrostatic linkages (to enhance film stability), while the weakly charged groups (maleic acid, MA) can alter multilayer film properties because they are responsive to external pH changes. In this study, we varied several assembly conditions such as pH, SS/MA ratio in PSSMA, and the ionic strength of the polyelectrolyte solutions. The multilayer films were also treated by immersion into pH 2 and 11 solutions after assembly. Quartz crystal microgravimetry and UV-visible spectrophotometry showed that the thickness of PSSMA/PAH multilayers decreases with increasing assembly pH regardless of whether salt was present in the polyelectrolyte solutions. When no salt was added, the multilayers are thinner, smoother, and grow less regularly. Atomic force microscopy images indicate that the presence of salt in polyelectrolyte solutions results in rougher surface morphologies, and this effect is especially significant in multilayers assembled at pH 2 and pH 11. When both polyelectrolytes are adsorbed at conditions where they are highly charged, salt was necessary to promote regular multilayer growth. Fourier transform infrared spectroscopy studies show that the carboxylic acids in the multilayers are essentially ionized when assembled from different pHs in 0.5 M sodium chloride solutions, whereas some carboxylic acids remain protonated in the multilayers assembled from solutions with no added salt. This resulted in different pH stability regimes when the multilayers were exposed to different pH solutions, post assembly.
authors.affiliation: Centre for Nanoscience and Nanotechnology, Department of Chemical and Biomolecular Engineering, The University of Melbourne, Victoria 3010, Australia.
authors.forename: Elvira
authors.initials: E
authors.lastname: Tjipto
authors.forename: John F
authors.initials: JF
authors.lastname: Quinn
authors.forename: Frank
authors.initials: F
authors.lastname: Caruso
mesh_terms: D004573:Electrolytes / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008298:Maleates / Q000737:chemistry*; D008567:Membranes, Artificial; D010316:Particle Size; D011137:Polystyrenes / Q000737:chemistry*; D012996:Solutions / Q000737:chemistry; D013499:Surface Properties
chemical_list: D004573:Electrolytes; D008298:Maleates; D008567:Membranes, Artificial; D011137:Polystyrenes; D012996:Solutions; C518261:poly(4-styrenesulfonic acid-co-maleic acid); C003321:polystyrene sulfonic acid; C030272:maleic acid