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.