Shift-time polyelectrolyte multilayer assembly: Fast film growth and high gas barrier with fewer layers by adjusting deposition time

In an effort to reduce deposition time and number of layers needed to achieve high gas barrier, multilayer films were deposited using 1 s exposures for the first four bilayers (BLs) and 1 min for subsequent dips. Thin-film assemblies of polyethylenimine (PEI) and poly(acrylic acid) (PAA) were deposited onto poly(ethylene terephthalate) [PET] using the layer-by-layer deposition process. Varying the exposure time of PET to polyelectrolyte solutions (i.e., dip time) significantly alters the growth rate of the multilayer thin films. The PEI/PAA system grows linearly with 1 s dip times and exponentially with longer times. Eight bilayers (650 nm) were required to achieve an undetectable oxygen transmission rate (<0.005 cm3/(m2·day)) using 1 min deposition steps, but this barrier was obtained with only 6 BLs (552 nm) using 1s deposition of the initial layers, reducing total deposition time by 73%. This “shift-time” concept makes layer-by-layer assembly much faster and more commercially feasible.