Growth and dynamics of polyelectrolyte multilayer thin films

Polyelectrolyte multilayer thin films adsorbed onto colloidal particles have been studied by solid-state nuclear magnetic resonance (NMR) spectroscopy in order to characterize the dynamic properties of the film components. In addition, the growth of the multilayer films was observed directly for the first time and quantification of the amount of polyelectrolyte adsorbed during each step was achieved. NMR relaxation measurements demonstrate that the polyions are more mobile when incorporated into a multilayer film than when in the bulk complex. The polycation, poly(diallyl dimethyl ammonium chloride) (PDADMAC) was found to exhibit greater mobility than the polyanion, poly(styrene-4-sulfonate) (PSS), becoming increasingly less mobile as layers were added to the multilayer assembly. Solid-state deuterium NMR further demonstrates the limited mobility of the PSS chain when incorporated into a multilayer film. No significant motion is observed on the kHz timescale under ambient conditions for PSS in a strong-strong polyelectrolyte film. However, a small mobile fraction, the result of loops and tails or chain ends is present when the multilayer films are exposed to humidity and salt solutions.; The behavior of the adsorbed water within this multilayer system was found to be dependent on the nature of the terminating layer. The changes in water mobility represent changes in the environment throughout the entire film, while the observed changes in the polymer dynamics are associated only with the surface layer. Additionally the water is found to be more closely associated with the polyanion, associating with the polycation only when it is the terminating layer. The behavior of the water for films comprised of a weak-strong polyelectrolyte combination are similar to that of the strong-strong multilayer system, when films are assembled with the polyions having high charge density. An increase in polyelectrolyte mobility is observed when the polyanion is the terminating layer in the poly(allylamine hydrochloride) (PAH)/poly(styrene-4-sulfonate) system, the reverse of what is observed in the strong-strong system. These differences are due to the differences in intrinsic mobility between the polyions within the multilayer film.; Finally multilayer films of PAH/PSS were prepared on alumina membranes and both the flux and selectivity could be controlled over a wide range, simply by varying the pH of the layer assembly and pH of the filtrate solution. Membranes assembled at pH 3 and pH 9 have water flux values which are dependent on the solution pH, while membranes assembled at pH 7 have constant flux regardless of filtrate solution pH. The selectivity for PAH/PSS modified membranes for dye molecules in pH 7 solutions was found to be the greatest and was the result of a combination of electrostatic and hydrophobic interactions of the polyelectrolyte chains at this pH value.