Figure 3. (A) Schematic illustration for the assembly of (TA@LDH/PEO)n films by LBL method; (B) UV-vis absorption spectra of the (TA@LDH/PEO)n (n=10−70) films on quartz glass substrates (inset: the linear relationship between the absorbance at 213 nm and the bilayer number n ); (C) Top-view and (D) cross-sectional SEM images of a (TA@LDH/PEO)50 film.
(TA@LDH/PEO)n multilayer films were fabricated through layer-by-layer technique on pre-treated substrates (Figure 3A). UV-vis spectra (Figure 3B) of the as-prepared (TA@LDH/PEO)n films show two intense absorption bands at 213 nm and 338 nm, attributed to the characteristic absorption of TA. The absorbance increases linearly (Figure 3B, inset) relative to the number of deposition cycles, illustrating the well-proportioned and gradual growth of the multilayer films. According to the molecular structure of PEO (Figure S3 C, Supporting Information) and TA (Figure 2B), hydrogen bond network can be formed in the (TA@LDH/PEO)n films.
Top-view SEM image of a (TA@LDH/PEO)50 film with a continuous and smooth surface is shown in Figure 3C. Clay alignment in the multilayer films is clearly observed using cross-sectional SEM (Figure 3D) image of 50 bilayer film deposited on silicon wafer with a thickness of ∼865 nm. The image shows a clear layered structure with LDH nanosheets shown in white lines, which illustrates good dispersity and high orientation of the LDH nanosheets. The 2D nanosheets with a perfect parallel orientation to the substrate will play the best role in the gas barrier function.