Barrier membranes with different sizes of aligned flakes

The permeability of polymer films can be reduced dramatically with many layers of thin mineral flakes aligned parallel to the film's surface. For a film with a volume fraction phi of flakes of aspect ratio alpha, the permeability reduction is expected to be proportional to alpha phi for the dilute limit (phi << 1 and alpha phi < 1) but proportional to (alpha phi)(2) in the semi-dilute limit (phi << 1 but alpha phi > 1). Permeabilities of hydrochloric acid and sodium hydroxide across films containing mica or vermiculite in polyvinyl alcohol agree with the second, semi-dilute prediction. Permeabilities of helium across films of montmorillonite in polyethylene glycol do as well. These improvements in barrier properties are independent of flake size, permeant and polymer chemistry. (c) 0 2005 Elsevier B.V. All rights reserved.