Flexible
transparent barrier films are required in various fields
of application ranging from flexible, transparent food packaging to
display encapsulation. Environmentally friendly, waterborne polymer–clay
nanocomposites would be preferred but fail to meet in particular requirements
for ultra high water vapor barriers. Here we show that self-assembly
of nanocomposite films into one-dimensional crystalline (smectic)
polymer–clay domains is a so-far overlooked key-factor capable
of suppressing water vapor diffusivity despite appreciable swelling
at elevated temperatures and relative humidity (R.H.). Moreover, barrier
performance was shown to improve with quality of the crystalline order.
In this respect, spray coating is superior to doctor blading because
it yields significantly better ordered structures. For spray-coated
waterborne nanocomposite films (21.4 μm) ultra high barrier
specifications are met at 23 °C and 50% R.H. with oxygen transmission
rates (OTR) < 0.0005 cm3 m–2 day–1 bar–1 and water vapor transmissions
rates (WVTR) of 0.0007 g m–2 day–1. Even in the most challenging environments (38 °C and 90% R.H.),
values as low as 0.24 cm3 m–2 day–1 bar–1 and 0.003 g m–2 day–1 were found for OTR and WVTR, respectively.
Upcoming
efficient air-borne wind energy concepts and communication
technologies applying lighter-than-air platforms require high-performance
barrier coatings, which concomitantly and nonselectively block permeation
not only of helium but also of ozone and water vapor. Similarly, with
the emergence of green hydrogen economy, lightweight barrier materials
for storage and transport of this highly diffusive gas are very much
sought-after, particularly in aviation technology. Here the fabrication
of ultraperformance nanocomposite barrier liners by spray coating
lamellar liquid crystalline dispersions of high aspect ratio (∼20 000)
silicate nanosheets mixed with poly(vinyl alcohol) on a PET substrate
foil is presented. Lightweight nanocomposite liners with 50 wt % filler
content are obtained showing helium and hydrogen permeabilities as
low as 0.8 and 0.6 cm3 μm m–2 day–1 atm–1, respectively. This exhibits
an improvement up to a factor of 4 × 103 as compared
to high-barrier polymers such as ethylene vinyl alcohol copolymers.
Furthermore, ozone resistance, illustrated by oxygen permeability
measurements at elevated relative humidity (75% r.h.), and water vapor
resistance are demonstrated. Moreover, the technically benign processing
by spray coating will render this barrier technology easily transferable
to real lighter-than-air technologies or irregular- and concave-shaped
hydrogen tanks.
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