ap0c00456_si_001.pdf (938.6 kB)
Impact of Ultraconfinement on Composite Barriers
journal contribution
posted on 2020-06-12, 15:33 authored by Theresa Schilling, Christoph Habel, Sabine Rosenfeldt, Maximilian Röhrl, Josef BreuFlexible optoelectronic
packaging is required to provide an ultrahigh
barrier to oxygen under ambient conditions, meaning at a relative
humidity above 50%. Many polymeric packaging materials, however, adsorb
water vapor and the consequential softening is detrimental for the
barrier properties. Despite its importance, systematic studies on
the impact of the relative humidity (RH) on the oxygen permeability
(OP) of clay nanocomposite barriers and convincing evidence for a
potential hydrophobization due to compounding with nanosheets are
scarce. Especially at filler contents greater than 30 vol %, as required
for ultrahigh barriers, a severe confinement is imposed on interlayered
polymer and thus its permeability properties are expected to be significantly
modified as compared to the bulk. A systematic study of the relation
between permeability and RH requires nanocomposite films that differ
in filler content but at the same time are comparable with respect
to aspect ratio, filler type, quality of texture, and one-dimensional
crystallinity. By applying water-soluble polyvinylpyrrolidone (PVP)
and ultrahigh-aspect-ratio synthetic clay (sodium fluorohectorite),
we were able to prepare hybrid samples that meet these requirements
for the first time. By spray coating, the components self-assemble
into hybrid films of one-dimensional crystalline Bragg stacks. Two
such hybrid films with filler contents of 31 and 40 vol % were fabricated.
Indeed, the filler content was found to greatly affect the dependence
of the oxygen permeability on RH. Comparing the performance of these
two films, the OP in the 40 vol % sample was four times lower than
would be expected because of the increase in filler content. To the
best of our knowledge, this is the first convincing evidence for a
pronounced confinement effect on the permeability.