Loading and release of methyl orange in layer-by-layer assembled polyelectrolyte films

The loading of methyl orange (MO) in layer-by-layer assembled thin films composed of poly(allylamine hydrochloride) (PAH) and poly(vinyl sulfate) (PVS) or poly(styrenesulfonate) (PSS) and its release from the films were studied. Anionic dye MO can be bound to the PAH-PVS and PAH-PSS films through electrostatic force of attraction. MO fully formed aggregates in the PAH-PVS films, while both monomeric and aggregated forms of MO were found in the PAH-PSS films. The loaded MO can be released from the films into buffer solutions. The release profiles significantly depended on pH and ionic strength of the medium in which MO was released. The release rate was faster in the basic solution than in neutral and acidic media. The release was accelerated in the media with higher ionic strength due to shielding of ionic interactions between MO and positive binding sites in the films.