Balancing polyelectrolyte diffusion and clay deposition for high gas barrier
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© 2016, ICE Publishing. All rights reserved. The use of clay nanoplatelets in layer-by-layer assembled thin films (50-200 nm thick) has been shown to reduce the oxygen transmission rates of polymer thick film substrates (>100 µm)bymany orders of magnitude.In an effort to reduce the thickness and number of deposited layers required to achieve high gas barrier, pH of the montmorillonite (MMT) clay aqueous suspension was reduced.Growth of a repeating sequence of polyethylenimine (PEI)/poly(acrylic acid) (PAA)/PEI/MMT is reduced when MMT pH was lowered from 10 to 6.This reduced pH causes the preceding PEI layer to be more charged, which causes more clay to bedeposited per layer.Just three PEI/PAA/PEI/MMT quadlayers (44 nm thick) exhibits an undetectable oxygen transmission rate (< 0.005 cm3/(m2day atm)) on a 179 µm thick PET substrate. As the clay deposition pH is altered, there is a compromise between high polymer diffusion (at pH 10) and high clay deposition that increases with decreasing pH. Clay at pH 6 provides the best compromise of dense packing and adequate spacing between layers.The 3 quadlayer film on PET exhibits an oxygen permeability ordersof magnitude below SiOxand metal thin films (<5 ×10-22cm3cm/(cm2s·Pa)).
author list (cited authors)
Hagen, D. A., Song, Y., Saucier, L., Milhorn, A., Stevens, B., & Grunlan, J. C.