Influence of Clay Platelet Spacing on Oxygen Permeability of Thin Film Assemblies

Thin films of anionic natural montmorrilonite clay and various polyelectrolytes have been produced by alternately dipping a plastic substrate into dilute aqueous mixtures containing each ingredient in an effort to show the influence of clay platelet spacing on thin film permeability. After polymer-clay layers have been sequentially deposited, the resulting transparent films exhibit a brick wall nanostructure comprised of completely exfoliated clay bricks in polymeric mortar. This brick wall forms an extremely tortuous path for a molecule to traverse, creating channels perpendicular to the concentration gradient that increase the molecule's diffusion length and delay its transmission. To a first approximation, greater clay spacing (i.e., reduced clay concentration) produces greater oxygen barrier. Oxygen transmission rates below 0.005 cm$^{3}$/m$^{2}\cdot $day have been achieved for films with only eight clay layers (total thickness of only 200 nm). With optical transparencies greater than 86{\%} and the ability to be microwaved, these thin film composites are good candidates for flexible electronics packaging and foil replacement for food.