Figure 6. (A) OTR of four different composite films:
(TA@LDH/PEO)50, (TA/LDH)50,
(LDH/PEO)50 and (TA/PEO)50; (B) OTR of
these composite films after stretching.
Three films (TA/LDH)50, (LDH/PEO)50 and
(TA/PEO)50 were prepared as control samples and compared
with (TA@LDH/PEO)50. As shown in Figure 6A, we can find
that the
(TA/PEO)50composite film shows the worst oxygen barrier ability, which is only 10×
lower than that of NR substrate at 50-bilayer (OTR =
311
cm3/(m2·24h·0.1MPa)). The reason why
(TA/PEO)50 composite films have poor oxygen barrier
ability than other films is due to the absence of LDH.
(TA@LDH/PEO)50 composite films have the best properties,
which might be because
(TA@LDH/PEO)50 has
better interfacial compatibility and richer hydrogen bond networks
than (TA/LDH)50(OTR = 124
cm3/(m2·24h·0.1MPa)) and
(LDH/PEO)50 (OTR =
128 cm3/(m2·24h·0.1MPa)). Hydrogen
bonded films can increase the diffusion residence of oxygen molecules
and enhance the barrier ability of the films. The OTR of other films
with various assembly numbers also shows that
(TA@LDH/PEO)n has the best performance
(Figure
S5, Support Information).
The morphology of these samples under different tensile conditions was
studied. When the stretch ratio is 25%, cracks appear in the
(LDH/PEO)50 film (Figure 7B), and the OTR increases by
53% (from 128 to 196
cm3/(m2·24h·0.1MPa)). At 120%
stretching, OTR increased by 404%. Similar to
(LDH/PEO)50 film,
the (TA/LDH)50film also exhibits a disappointing oxygen barrier after stretching.
However, the stretch ratio of (TA/LDH)50 film is better
than that of (LDH/PEO)50. Cracks appeared at 50%
tension (Figure 7E) and OTR reached
210.03cm3/(m2·24h·0.1MPa). Although
the oxygen resistance of (TA/PEO)50 thin films is poor,
its tensile properties are excellent. Only when the stretch ratio
reaches 120% (Figure 6J), the small cracks appear. At this time, its
OTR increased by 31%. TA effectively acts as a small molecule
cross-linker between flexible PEO chains, posing very little restriction
to chain segment mobility within the TA/PEO assembly. The non-rigid
hydrogen bonding network between TA and PEO provides excellent tensile
properties. Similarly, the (TA@LDH/PEO)50 film also has
small cracks when stretched by 120%. The oxygen barrier ability of
(TA@LDH/PEO)50 film is much higher than that of
(TA/PEO)50 film, while these two films show similar
stretchability. The excellent properties of
(TA@LDH/PEO)50 films are attributed to the bridging
effect of TA at the interface of LDH and PEO, which provide stretchable
elastic network to tolerate the external force.