as evidenced by the following SEM observation.
Fig. 3 shows the SEM images of the cotton samples. For the untreated pristine cotton fabric, the fabric weave structure and native striations along the fiber can be clearly observed (Fig. 3a and b). When the surface was assembled with 1 or 3 layers of PAH/SiO2, silica nanoparticles were found to partially cover the fiber sur- face at random (Fig. 3c and d). This can be used to explain the above FTIR analysis. Five layers of PAH/SiO2 assembly resulted in homogeneous coverage of silica nanoparticles on the cotton fibers (Fig. 3e). When the fabric was coated with 7 layers of PAH/SiO2, more nanoparticles were assembled and they aggregated on the cotton fibers (Fig. 3f).
XPS measurement was used to examine the chemical composi- tion of the coated fabric surface. For the untreated pristine cotton fabric, only peaks corresponding to C and O were observed, as shown in Fig. 4a. When the fabric was assembled with (PAH/SiO2)5 multilayers, two more distinctive peaks appeared at 153 and 102eV, which are attributed to Si 2s and Si 2p, respectively. In addition, the N 1s originating from the PAH layers was detected at 398 eV. This measurement confirmed the assembly of positively charged PAH and negatively charged silica nanoparticles on the cot- ton fibers. After being modified with FAS, new peaks with binding energies of 833, 687 and 291 eV appeared, corresponding to F KLL, F 1s, and C 1s of FAS, respectively (Fig. 4c).
Fig. 5 shows the TGA curves of the fabrics. The thermal decomposition mainly occurred in a narrow temperature range of 300–370◦C and the cotton fabrics assembled with silica nanopar- ticles showed slightly higher thermal stability compared to the untreated fabric. When the untreated cotton fabric was heated to 600◦C at a rate of 10◦C/min, only 14% of the original weight remained. When the silica nanoparticles were assembled to the fiber surface, the same heating condition resulted in 20% remain- ing weight. The remaining weight percentage was further increased to 24% after the coated fabric was modified with FAS. These results confirmed the incorporation of silica nanoparticles and FAS onto the cotton fibers.