Predictive tools for selection of appropriate polyelectrolyte multilayer film for the functionalization of organic membranes

• Selection of appropriate PES solvent using Hansen theory.
• In situ investigations of multilayer growth on model PES surface.
• Functionalization of PES membrane by polyelectrolyte multilayer.

Layer-by-layer adsorption of oppositely charged polyelectrolytes is a suitable method to improve the filtration properties of polyethersulfone (PES) membrane. Therefore, a weak polycation (poly(allylamine hydrochloride, PAH) was combined with either a weak polyanion (polyacrylic acid, PAA) or a strong polyanion (polystyrene sulfonate, PSS) to create a polyelectrolyte multilayer film (PEM) of 11 layers. Adsorption of the polyelectrolytes was performed using saline solutions at native pH or pH 6. The growth of (PAH-PAA)n or (PAH-PSS)n multilayer film was monitored in situ by optical reflectometry (OR) and quartz crystal microbalance (QCM-D). At the end of the build-up, a rinsing step at pH 2 was done to test the stability of the film at the filtration conditions. The rinsing step did not lead to desorption of the (PAH-PSS)n multilayer. On the contrary, films made of PAH and PAA were strongly affected, but did not entirely disassemble by changing the pH. Filtration efficiency of PEM-modified membrane was finally investigated by filtrating copper ions solution. These membranes were alternately immersed into polyelectrolyte solutions during 10 min to achieve the functionalization. As predicted by the OR and QCM-D results, a good retention of copper cations was recorded for (PAH-PAA)n modified membrane. On the contrary, a poor retention was observed for membrane modified by (PAH-PSS)n multilayer despite their good behavior during the filtration step. This could be attributed to a different wall pores modification.

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