The addition of TiO nanoparticles to the FEVE coating
The addition of TiO2 nanoparticles to the FEVE coating was expected to generate self-cleaning properties that can expand its application range. We investigated the self-cleaning properties of the composite coating by the test method described in Section 2.4 and the results are shown in Fig. 6. As shown in Fig. 6(a), the WCA of PTFE/FEVE and modified TiO2-PTFE/ FEVE coating had almost the same value even after UV-light irradiation, whereas the TiO2-PTFE/FEVE coating was gradually converted to a hydrophilic state. Figs. 6(b) and 6(c) show that after the adhesion of oleic MG-262 as a representative contaminant, the WCA of each composite coating immediately decreased to around 63°. Once the surface was, the hydrophobicity of PTFE/FEVE was hardly recovered without cleaning by organic solvent. Under UV-light irradiation, the hydrophilic state of TiO2-PTFE/FEVE was recovered by the effect of photo-induced hydrophilicity. By contrast, oleic acid was successfully removed only on the modified TiO2-PTFE/FEVE composite coating surface after UV-light irradiation for 7 h, after which the contact angle gradually increased and finally recovered to its initial value. Even after five cycles of adhesions of oleic acid and UV-light irradiation, the composite coating surface recovered its good hydrophobic state as shown in Fig. 6(d). The mechanism underlying the photocatalytic degradation of oleic acid on TiO2 nanocomposite films has been researched and analysed ,  and . Thus, the removal effect of oleic acid was achieved by the photocatalytic self-cleaning property of TiO2 nanostructures. The functional coating of modified TiO2-PTFE/FEVE realised the sufficiently hydrophobic surface with an efficient photocatalytic self-cleaning effect.