Layer-by-layer self-assembly of alumosilicate-polyelectrolyte composites: Mechanism of deposition, crack resistance, and perspectives for novel membrane materials

The morphology and gas permeation properties of montmorillonite-polyelectrolyte self-assembled multilayer systems have been investigated. Without any special pretreatment, a stable film of montmorillonite-polymer composite was assembled on a hydrophobic poly(ethyleneterephthalate) support by means of layer-by-layer deposition. Al individual alumosilicate platelets were found to be oriented in parallel to the substrate, while their surface density strongly depended on the nature of the polyelectrolyte (charge and molecular weight). The organic-inorganic films were found to be very flexible and crack-resistant even under a considerable mechanical stress. This opened a possibility to preclude gas diffusion through defects and to design highly selective ultrathin membranes. A permeation rate of oxygen was found to decrease 6.6 times for ca. 200 nm montmorillonite/poly(diallyldimethylammonium) chloride film, while a permeation rate of aqueous vapors did not change at all. This effect was attributed to the dominance of solution/adsorption permeation mechanism over the Knudsen diffusion. This fact made the montmorillonite-polyelectrolyte multilayers stand out among other thin films for which the diffusion through defects was found to be the primary mechanism of gas permeation. This finding demonstrated both practical and fundamental importance of hybrid thin films that combined the properties of both organic and inorganic materials.