## 3 Results and Discussion
### Superhydrophobic Property and Environmental Durability  
To evaluate the wettability properties of HNTs samples, the contact angle (CA) and sliding angle (SA) were tested by releasing water droplets of defined volume on the surface of flattened HNTs powders, and micrographs were recorded by CCD camera, as shown in Figure 6. The CA values of P-HNTs were less than 10\({}^{\circ}\) (Figure 6a), indicating that the pure halloysite was hydrophilic. When coating PDA on HNT surface, the CA increased to 46.7 \(\pm\) 3.1\({}^{\circ}\) (Figure 6b), which was similar to the reported CA values of 46.9\({}^{\circ}\)[31]. After the following reaction for grafting long-chain alkylamine, the surface property of HNT was changed from hydrophilic to hydrophobic, with CA values of 112.3 \(\pm\) 3.3\({}^{\circ}\) (Figure 6d). Interestingly, with the help of VM, the mean CA values of VM/PDA-HNTs (57.2 \(\pm\) 4.3\({}^{\circ}\), Figure 6c) were marginally higher than these of PDA-HNTs. Correspondingly, the highest CA values of 156.3 \(\pm\) 2.3\({}^{\circ}\) (Figure 6e) were observed in VM/ODA-HNTs with SA values of 4.5 \(\pm\) 0.4\({}^{\circ}\) (Figure 6f), demonstrating that the resultant superhydrophobic surface was finally achieved. It may be ascribed to the self-assembly of VM, forming a columnar structure that can act as a template to induce PDA nodules in the vertical direction, thus creating rough PDA coatings on the surface of HNTs [39; 40]. In addition, the anti-water long-chain alkyl groups were grafted onto this rough surface. Consequently, the resultant superhydrophobic structures were successfully built on the HNTs, as illustrated in Scheme 1. Figure 5: X-ray photoelectron spectroscopy (XPS) wide-scan and high resolution spectra of HNTs samples. (**a**) wide-scan XPS spectra of PDA-HNTs and ODA-HNTs; (**b**) C 1s core-level of PDA-HNTs; (**c**) N 1s core-level of PDA-HNTs; (**d**) N 1s core-level of ODA-HNTs. Figure 7a exhibits the changes of CAs on the surface of flattened HNTs powders samples over time. The CAs on P-HNTs decreased quickly in 15 s, and slowly reached the equilibrium in the next 60 s. After coating PDA on HNT surface, the water resistance performance of PDA-HNTs became better at the beginning of the contact in comparison with the pure one. However, with time going on, the CAs continued to decline in 150 s, and finally got to the minimum value below 10\({}^{\circ}\). These results suggested that simple dopamine as a modifier can hardly generate the hydrophobic layers on HNT surface, which was ascribed to the hydrophilic groups (e.g., amino, hydroxyl) existing on the PDA molecule [30]. The CAs of ODA-HNTs decreased from about 120\({}^{\circ}\) to 110\({}^{\circ}\) in 150 s, which presented hydrophobic performance. In the case of VM, the CAs on VM/ODA-HNTs surfaces exhibited no apparent change for this period of time, and all were maintained over 150\({}^{\circ}\) after 150 s. These phenomena can be easily observed in the optical photographs. When dropped on the hydrophilic HNTs surface (separate samples of P-HNTs, PDA-HNTs, and VM/PDA-HNTs), the water droplets immersed into the powders, leaving an agglomerated and wet surface (Figure 7b-d). In contrast, the water droplets remained their round shape on the hydrophobic HNTs surface (Figure 7e,f). Especially, the spherical water spot similar to that on lotus leaf was founded on the VM/ODA-HNTs surfaces. To evaluate the environment durability performance of superhydrophobic HNTs, various tests were conducted corresponding to different harsh conditions. As shown in Figure 8a, the CAs of VM/ODA-HNTs were all maintained above 150\({}^{\circ}\) after immersing these superhydrophobic samples into diverse chemical conditions including solutions of HCl (pH = 3) and NaOH (pH = 11), acetone, ethanol, dioxane, and trichloromethane (TCM) for 24 h at room temperature, and boiling water for 3 h, which demonstrated the resultant superhydrophobic HNTs had great chemical resistances.