Flexible and transparent polymeric "superbarrier" packaging materials have become increasingly important in recent years. Layer-by-layer assembly offers a facile technique for the fabrication of layered, polymer-clay superbarrier thin films. At only 51 nm thick, these nanocomposite thin films, comprised of 12 polymer and 4 clay layers, exhibit an oxygen permeability orders of magnitude lower than EVOH and SiOx. Coupling high flexibility, transparency, and barrier protection, these films are good candidates for a variety packaging applications.

Super gas barrier thin films, fabricated with layer-by-layer assembly of polyethylenimine and graphene oxide, exhibit significantly reduced oxygen and carbon dioxide transmission rates. This thin film's nanobrick wall structure also provides high gas selectivity for hydrogen.

Thin films of sodium montmorillonite clay and branched polyethylenimine (PEI) are deposited on various substrates using layer-by-layer assembly. Films with 40 polymer-clay layers contain more than 84 wt% clay, have hardness as high as 1 GPa, and are completely transparent. Oxygen transmission rates (OTR) through these films decrease as the pH of PEI increases. These pH-tailorable properties are the result of changing PEI charge density, which causes the polymer to deposit more thickly at high pH because of low charge density. After 70 PEI (at pH 10)-clay layers are deposited onto 179 µm poly(ethylene terephthalate) film, the resulting 231 nm assembly has an OTR below the detection limit of commercial instrumentation (<0.005 cc/(m 2 day atm)). When multiplied by thickness, the resulting oxygen permeability is found to be less than 0.002 × 10 -6 cc/(m day atm)), which is lower than values typically reported for SiOx. This is the lowest permeability ever reported for a polymer-clay composite and is believed to be due to a brick wall nanostructure created by the alternate adsorption of polymeric mortar and highly oriented, exfoliated clay platelets. Because of their high level of transparency and gas barrier, these films are good candidates for a variety of flexible electronics, food, and pharmaceutical packaging.

Layer-by-layer (LbL) assembly has emerged as the leading non-vacuum technology for the fabrication of transparent, super gas barrier films. The super gas barrier performance of LbL deposited films has been demonstrated in numerous studies, with a variety of polyelectrolytes, to rival that of metal and metal oxide-based barrier films. This Feature Article is a mini-review of LbL-based multilayer thin films with a 'nanobrick wall' microstructure comprising polymeric mortar and nano-platelet bricks that impart high gas barrier to otherwise permeable polymer substrates. These transparent, water-based thin films exhibit oxygen transmission rates below 5 × 10(-3) cm(3) m(-2) day(-1) atm(-1) and lower permeability than any other barrier material reported. In an effort to put this technology in the proper context, incumbent technologies such as metallized plastics, metal oxides, and flake-filled polymers are briefly reviewed.

The influence of the clay deposition suspension concentration on gas barrier thin films of sodium montmorillonite (MMT) clay and branched polyethylenimine (PEI), created via layer-by-layer assembly, was investigated. Films grown with MMT suspension concentrations ranging from 0.05 to 2.0 wt % were analyzed for their growth as a function of deposited polymer-clay bilayers (BL) and their thickness, clay concentration, transparency, nanostructure, and oxygen barrier as a function of the suspension concentration. The film thickness doubles and the visible light transmission decreases less than 5% as a function of MMT concentration for 20-BL films. Atomic force and transmission electron microscope images reveal a highly aligned nanobrick wall structure, with quartz crystal microbalance measurements revealing a slight increase in the film clay concentration as the MMT suspension concentration increases. The oxygen transmission rate (OTR) through these 20-BL composites, deposited on a 179 μm poly(ethylene terephthalate) film, decreases exponentially as a function of the MMT clay concentration. A 24-BL film created with 2.0 wt % MMT has an OTR below the detection limit of commercial instrumentation (<0.005 cc/m(2)·day·atm). This study demonstrates an optimal clay suspension concentration to use when creating LbL barrier films, which minimizes deposition steps and the overall processing time.