Influence of LbL surface modification on oxygen cross-over in self-assembled thin composite membranes

The paper is concerned with the investigation of oxygen transport in layer-by-layer (LbL) self assembly of polystyrene sulfonic acid sodium salt (PSS) and polyallylamine hydrochloride (PAH) on Nafion membrane depending on the number of deposited bilayers, ion type within the multilayers and temperature. It is observed from SEM analysis that the polyelectrolyte layers growth on each side of Nafion membrane regularly. The oxygen permeability image of (PAH–PSS)20 is 691 cm3/(m2 day bar) at 25 °C while image of pristine Nafion is 2329 cm3/(m2 day bar) at the same temperature. This significant reduction (70.3%) in gas permeability can be explained by the formation of LbL multilayers which both restrict the mobility of gas through the polymer matrix and adjust gas solubility properties in conjunction with ion–dipole interaction between the polar phase of Nafion and the secondary ammonium groups of PAH. (PAH/PSS)20–Na+ and (PAH/PSS)20–H+ exhibit 64.4% and 52.3% reduction in oxygen permittivity at 25 °C in comparison with the pristine Nafion®117, respectively, while the proton conductivities of these membranes are 106.9 and 136.9 mS/cm. Promisingly, it is found that the membrane selectivity values (Φ) of all multilayered membranes in both H+ and Na+ form are much higher than that of perfluorosulfonated ionomer. The thickness of deposited bilayers dominates the diffusion and solubility properties of oxygen through the composite membrane while the major effect of surface hydrophilicity is not observed on oxygen permeability.