Combined Ionic and Hydrogen Bonding in Polymer Multilayer Thin Film for High Gas Barrier and Stretchiness

A unique polymer multilayer thin film with high gas barrier at high strain (>10%) was achieved with a combination of ionic and hydrogen bonding. Layer-by-layer assembly was used to deposit quadlayers (QL) of polyethylenimine (PEI), poly(acrylic acid) (PAA), poly(ethylene oxide) (PEO), and PAA. Altering the deposition pH of the various layers resulted in different physical and mechanical properties. PEI/PAA/PEO/PAA quadlayers assembled at pH 10/4/2.5/2.5 grow much thicker than the same film with all components deposited at pH 3, which is due to a porosity transition during assembly and in-and-out diffusion of the partially charged polyelectrolytes with high chain mobility (PEI at pH 10 and PAA at pH 4). The change in pH during the film assembly induces a porous structure in the 10/4/2.5/2.5 film that results in poor gas barrier. Films deposited on 1 mm thick polyurethane rubber at pH 3 have a densely packed structure with no pores. A 20 QL film (∼1 μm thick) achieves an oxygen transmission rate 15 times lower than uncoated rubber due to the synergistic effect of the interdigitated layers of ionic and hydrogen bonding. When stretched 10%, the barrier improves by a factor of 28 relative to uncoated polyurethane. This combination of stretchability and high gas barrier is unprecedented and offers the opportunity to produce relatively high barrier elastomers.