Ordered polyelectrolyte multilayers. 6. Effect of molecular parameters on the formation of hybrid multilayers based on Poly(Diallylammonium) salts and exfoliated clay

A new series of poly(diallylammonium) salts with varying hydrophilic-hydrophobic balance and bulkiness was prepared, to investigate the impact of these parameters on the formation of electrostatic layer-by-layer assemblies. The polycations were self-assembled on quartz and silicon substrates together with Laponite, a synthetic, negatively charged alumino-silicate clay. This system was found to be quite robust for forming lamellar heterostructures of controlled thickness at the solid interfaces. Bulky and hydrophobic, as well as amphiphilic, polycations can be accommodated between the rigid exfoliated aluminosilicate platelets without disrupting the lamellar-like structure. Ellipsometry and X-ray reflectivity showed that substituents attached to the backbone have a significant impact on both the growth process and the extent of the ordered region. Hydrophobicity and bulkiness favored the formation of thicker films, presumably due to the more coily conformation of the polycation during the deposition. Films are only partially organized and coherence lengths along the normal of the plane are in the range 2.7-7.5 nm. The values depend sensitively on the detailed chemical structure of the polyelectrolyte employed and the nature of the solvent used for the deposition process.