Multilayer Polyelectrolyte Deposition

PAH (10⁻² mol/L) and PSS (10⁻² mol/L) were used as polyelectrolyte solutions. The pH for the PAH solutions was adjusted to 4 because this polyelectrolyte was fully ionized at this value.
The multilayer deposition of PEL layers was carried out by ND Multi Axis Dip Coaters ND-3D 11/5 (Nadetech, Noáin (Navarra), Spain) with a wide speed immersion range (from 1 mm∙min⁻¹ to 2000 mm∙min⁻¹). The membrane was clamped on a special support and immersed into solutions for different times. The procedure was as follows (shown in Figure 1): firstly, the membrane was deposited into a polycation solution of PAH for 10 min. Next, it was removed and rinsed thoroughly with water for 1 s 15 times, 5 s three times, and 15 s one time, successively. Then, the membrane was immersed in PSS solution for 10 min, after which the same water rinsing process of the membrane was repeated. In this way, one PEL bilayer was created on the membrane surface. The required number of additional bilayers was deposited according to a similar scheme. When the PAH polycation was previously introduced into the PVA matrix, the PSS polyanion would be firstly deposited on the membrane surface. The optimum number of PEL bilayers applied to the surface of the membrane was 10, because the deposition of fewer or more than 10 bilayers did not lead to the improvement of membrane transport properties [23 (link)].