Improving oxygen barrier and reducing moisture sensitivity of weak polyelectrolyte multilayer thin films with crosslinking

Abstract

Thin films of polyethylenimine (PEI) and poly(acrylic acid) (PAA), deposited using layer-by-layer assembly, were studied to understand the influence of various crosslinking methods on their oxygen and water vapor barrier. Glutaraldehyde (GA), 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide methiodide (EDC) and thermal crosslinking were evaluated with respect to film thickness and barrier properties. The thickness of an 8 bilayer PEI/PAA assembly decreased from 640 to 551 nm after crosslinking with a 0.1 M aqueous GA solution and obtained an oxygen permeability one order of magnitude better than an SiO_x thin film (<5.9 × 10⁻²¹ cm³ cm cm^¬2 s^¬1 Pa^¬1) This same crosslinking treatment reduced the oxygen transmission rate (OTR), measured at 23 °C and 100% RH, from 0.61 to 0.09 (cm³ m⁻² day^¬1). Increasing the number of bilayers and heating time with thermal crosslinking also reduces the water vapor transmission rate (WVTR). These nanocoatings are a promising alternative to currently used barrier layers for flexible electronics and food packaging.