Improving gas barrier of clay-polymer multilayer thin films using shorter deposition times

Relatively fast exposure times (5 s) to aqueous solutions were found to improve the gas barrier of clay-polymer thin films prepared using layer-by-layer (LbL) assembly. Contrary to the common belief about deposition time (i.e., “the longer the better”), oxygen transmission rates (OTRs) of these ‘nanobrick wall’ assemblies are improved by reducing exposure time (from 1 min to 5 s). Regardless of composition, LbL films fabricated using shorter deposition time are always thicker in the first few layers, which correspond to greater clay spacing and lower OTR. A quadlayer (QL) assembly consisting of three repeat units of branched polyethylenimine (PEI), polyacrylic acid (PAA), PEI and montmorillonite (MMT) clay is only 24 nm thick when deposited with 1 min exposure to each ingredient. Reducing the exposure time of polyelectrolytes to 5 seconds not only increases this film thickness to 55 nm, but also reduces the oxygen transmission rate (OTR) to 0.05 cm³/(m²·day·atm), which is two orders of magnitude lower than the same film made with 1 min exposures. A conceptual model is proposed to explain these differences in growth and barrier, which are linked to polyelectrolyte relaxation, desorption, and interdiffusion. The universality of these findings is further exemplified by depositing clays with varying aspect ratio. This ability to quickly deposit high barrier nanocomposite thin films opens up a tremendous opportunity in terms of commercial scale processing of layer-by-layer assemblies.