High gas barrier imparted by similarly charged multilayers in nanobrick wall thin films
For the first time, super oxygen barrier thin films have been deposited using two successive anionic layers, sodium montmorillonite clay (MMT) and poly(acrylic acid) (PAA), following every cationic layer of polyethylenimine (PEI) during layer-by-layer assembly. PEI/MMT bilayer films show good oxygen barrier due to a nanobrick wall structure, consisting of exfoliated clay nanoplatelets within polymeric mortar. PAA as a third component is hydrogen bound with MMT and heals any vacancies left by desorbed clay platelets. This added layer densifies the film and increases barrier performance by at least one order of magnitude. Performance is further improved by using high molecular weight PEI, where oxygen transmission rates (OTR) below the detection limit of commercial instrumentation (<0.005 cm3/m2·day·atm) are achieved with a thin film of only 10 trilayers (62 nm). These super gas barrier, transparent nanocoatings are useful for a variety of food, pharmaceutical, and flexible elctronics packaging applications.