(645g) High Gas Barrier Polymer-Clay Nano Brick Wall Thin Films

Thin films of sodium montmorillonite clay and weak polyelectrolytes were prepared by alternately dipping a PET substrate into four different dilute aqueous mixtures (polyethylenimine, poly(acrylic acid), polyethylenimine, and montmorrilonite clay).   After depositing four of these quadlayers (QL), the resulting transparent film exhibits an oxygen transmission rate below the detection limit of commercial instrumentation (< 0.005 cm³/m² day).  This level of oxygen barrier, which is unprecedented for a clay-filled polymer composite, is believed to be due to a nano-brick wall microstructure comprised of completely exfoliated clay bricks in polymeric mortar and clay layer spacing on the order of tens of nanometers.  This 4 QL film has a thickness of only 51 nm and an optical transparency of 95%.  When multiplying OTR by film thickness to achieve oxygen permeability, we find that these films are a better barrier than SiO_x and also rival metalized plastic film.  Some all-polymer assemblies with nearly equivalent gas barrier will also be mentioned.  These thin film composites could be a microwaveable foil replacement for a variety of food packaging applications.