Kevin M. Holder

Influence of Clay Concentration on the Gas Barrier of Clay–Polymer Nanobrick Wall Thin Film Assemblies

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.

Transparency, Gas Barrier, and Moisture Resistance of Large-Aspect-Ratio Vermiculite Nanobrick Wall Thin Films

The ability to incorporate large-aspect-ratio vermiculite (VMT) clay into thin films fabricated using the layer-by-layer assembly techinique is reported for the first time. Thin films of branched polyethylenimine (PEI) and VMT were analyzed for their growth rate, clay composition, transparency, and gas barrier behavior. These films consist of >96 wt% clay, are >95% transparent, and, because of their nanobrick wall structure, exhibit super gas barrier behavior at thicknesses of <165 nm. When coupled with flexibility, the optical clarity and super barrier that these coatings can impart make them superb candidates for a variety of packaging applications.

Stretchable Gas Barrier Achieved with Partially Hydrogen-Bonded Multilayer Nanocoating

Super gas barrier nanocoatings are recently demonstrated by combining polyelectrolytes and clay nanoplatelets with layer-by-layer deposition. These nanobrick wall thin films match or exceed the gas barrier of SiOx and metallized films, but they are relatively stiff and lose barrier with significant stretching (≥ 10% strain). In an effort to impart stretchability, hydrogen-bonding polyglycidol (PGD) layers are added to an electrostatically bonded thin film assembly of polyethylenimine (PEI) and montmorillonite (MMT) clay. The oxygen transmission rate of a 125-nm thick PEI-MMT film increases more than 40x after being stretched 10%, while PGD-PEI-MMT trilayers of the same thickness maintain its gas barrier. This stretchable trilayer system has an OTR three times lower than the PEI-MMT bilayer system after stretching. This report marks the first stretchable high gas barrier thin film, which is potentially useful for applications that require pressurized elastomers.

A review of flame retardant nanocoatings prepared using layer-by-layer assembly of polyelectrolytes

As flammable polymeric materials become more ubiquitous in consumer goods, home furnishings, and transportation, there is a growing need for safe and effective flame retardant treatments. Recent studies suggest that certain flame retardant chemistries exhibit environmental and health problems, which has prompted the development of new flame retardant technologies. Layer-by-layer assembly has emerged as a promising technique for depositing environmentally-benign flame retardants on a variety of polymeric substrates. This technology has allowed the translation of common flame retardant mechanisms onto the surfaces of flammable polymers in the form of nanometer-scale coatings. Significant reductions in heat release rates and smoke release, as well as the ability to self-extinguish in open flame tests, have been observed on a variety of substrates. This review provides a comprehensive description of flame retardant multilayer nanocoatings on textiles, foams, and bulk polymers, as well as insight into the future direction of this growing field.