## 3 Results and Discussions
### Surface Structure Analysis for MWCNTs  
The MWCNTs-alkyne was obtained via two gentle reaction processes, including acylchlorination and esterification, during which MWCNT-COOH was reacted with excess thionyl chloride to obtain a high esterification reaction efficiency COCL group, and the COCL group was then reacted with excess propargyl alcohol to get a complete surface coverage of the functional MWCNTs. FT-IR was performed on original and functionalized MWCNTs, and their corresponding spectra are shown in Figure 6. For the MWCNTs-COOH, the IR spectrum shows two absorption bands at 1740 cm\({}^{-1}\) (corresponding to stretching vibrations of carbonyl groups C=O) and 1635 cm\({}^{-1}\) (assigned to conjugated C=C stretching). MWCNTs-alkyne exhibits the same bands with the addition of an intensity band at 2100 cm\({}^{-1}\) (the alkyne group) [27]. Azido-terminated PMMA presents a typical absorption band at 2100 cm\({}^{-1}\) (-N\({}_{3}\) group), which suggests that the subsequent click reaction can be performed. After the click reaction, the new absorptions peak appeared at 1110 cm\({}^{-1}\), and 1020 cm\({}^{-1}\), which was the C-O-C  
Figure 4: Grafting percentage of the azide/alkyne modified MWCNT. Figure 5: TGA results of pristine MWCNTs (**a**) MWCNTs-alkyne (**b**) MWCNTs-\(g\)-PMMA (**c–e**) polymerization for 6, 12, and 18 h, respectively. group in the ester group of the PMMA grafted onto the surface of MWCNTs. The click combination of the alkyne-functionalized MWCNTs and azide-functionalized PMMA provided a 1,2,3-triazole ring. This suggests that the PMMA molecule is successfully grafted onto the surface of the MWCNTs. Thus, the IR spectra of the MWCNTs-PMMA nanohybrid, featuring an alkyne peak of MWCNTs at 2100 cm\({}^{-1}\), entirely disappeared, revealing the formation of 1,2,3-triazole after the click reaction. Figure 7 shows the Raman spectra of pristine MWCNTs, MWCNTs-COOH, MWCNTs-alkyne, and MWCNTs-\(g\)-PMMA. The characteristic peaks at 1343 cm\({}^{-1}\) and 1585 cm\({}^{-1}\) correspond to the D (tangential band) and G (disorder band) peaks of carbon nanotubes, respectively [22]. The D band is due to a disordered graphite structure or sp\({}^{3}\)-hybridized carbons of the nanotubes, whereas the G band refers to a splitting of the E2g stretching mode of graphite [28; 29]. The peak intensity D and G band ratios (I\({}_{\rm D}\)/I\({}_{\rm G}\)) for MWCNTs-COOH, MWCNTs-alkyne, and MWCNTs-\(g\)-PMMA are higher than those of the pristine MWCNTs, which suggests that alkyne-decoration and the click reaction successfully functionalize MWCNT. Figure 8 depicts the TEM photographs of pristine MWCNTs, carboxyl functionalized, and MWCNTs-\(g\)-PMMA. After the acid treatment, the closed end opening of the nanotube can be observed. The pristine MWCNTs generally present closed caps and cylindrical walls, which are uncapped and have rough \"convex-concave\" walls after the partial oxidation treatment [30]. These disfigurements improve the specific surface area and pore volume of the oxidized MWCNTs [31]. On the other hand, after the PMMA segments are grafted onto the surface of nanotubes by the click reaction, a thicker diameter of the MWCNTs-\(g\)-PMMA is observed. Figure 6: FT-IR spectra of pristine MWCNTs, MWCNTs-COOH, MWCNTs-alkyne, PMMA-N\({}_{3}\), and MWCNTs-\(g\)-PMMA (GP = 22.0%). Figure 7: Raman spectra of pristine MWCNT, MWCNTs-COOH, MWCNTs-alkyne, and MWCNTs-g-PMMA (GP = 22.0%). Figure 9 shows the dispersion images of MWCNTs-\(g\)-PMMA in comparison with the pristine MWCNTs in water. After the ultrasonic treatment of these two dispersing solutions, the pristine MWCNTs could not disperse and stably suspended well in water because of the strong intrinsic van der Waals forces between them [13]. After two hours of standing, the pristine MWCNTs are obviously aggregated. However, the MWCNTs-\(g\)-PMMA can maintain its stable dispersion, even after 24 hours. This means that grafted PMMA has effectively reduced the apparent activation energy of MWCNTs, which can prevent the aggregation phenomenon.