Figure 4. (A) OTR of (TA@LDH/PEO)n (n =10-70) films with different bilayer numbers; (B) Schematic diagram of gas penetration in a barrier film.
The bare NR substrate displays an oxygen transmission rate (OTR) of 3190 cm3/(m2·24h·0.1MPa), as shown in Figure 4A. Upon deposition of (TA@LDH/PEO)ncoatings, the OTR values undergo a significant decrease. With an increase in the number of the assembly layers, the permeability decreases because of the barrier effect caused by horizontal LDH nanosheets. The improved oxygen barrier properties are attributed to the good 2D ordering of LDH nanosheets, which increases the diffusion path of oxygen molecules, commonly known as tortuous pathway (Figure 4B). The best oxygen resistance performance can be obtained when the composite film has 50 layers (OTR = 110 cm3/(m2·24h·0.1MPa)). When the number of (TA@LDH/PEO)n film layers continues to increase, the oxygen barrier performance begins to decline. This is probably because when there are too many layers and the film is too thick, the substrate will be hard to bear so that the composite film will fall out or crack. Therefore, 50 layers are selected as the best number of bilayers.