Correlation of the swelling and permeability of polyelectrolyte multilayer films

Alternating adsorption of polycations and polyanions on porous supports yields a variety of size-selective membranes whose swelling and transport properties depend on constituent polyelectrolytes, capping layer choice (polycation or polyanion), and deposition conditions. This report shows that in aqueous experiments, ellipsometrically determined swelling percentages correlate well with nanofiltration (NF) rejections and diffusion dialysis fluxes. For example, hyaluronic acid (HA)/chitosan films swell 4 times more than poly(styrene sulfonate) (PSS)/poly(allylamine hydrochloride) coatings, and in NF experiments, the HA/chitosan membranes permit a 250-fold greater fractional passage of sucrose. In general, films prepared from polyelectrolytes with a high charge density show low swelling and slow solute transport, presumably because of a high degree of ionic cross-linking. In the case of PSS/poly(diallyldimethylammonium chloride) (PDADMAC), PDADMAC-capped films can swell 4-fold more than their PSS-terminated counterparts, and as would be expected, glucose and sucrose transport rates in diffusion dialysis are about 1.7- and 17-fold more, respectively, when these films end in PDADMAC. Polyelectrolyte multilayers also exhibit wide-ranging swelling properties in ethanol, but transport rates do not correlate with ethanol uptake. In this solvent, the density of ionic cross-links and film hydrophobicity likely exert opposite effects on swelling, which could complicate the correlation between swelling and transport.