Formation of photo- and thermo-stable layered double hydroxide films with photo-responsive wettability by intercalation of functionalized azobenzenes

A hybrid film containing a substituted azobenzene, 7-[(trifluoromethoxyphenylazo)phenoxy]pentanoate anion (CF3AZO-)(CF3AZO-), intercalated in a layered double hydroxide (LDH) film immobilized on a porous anodic alumina/aluminum (PAO/Al) substrate has been prepared by an anion-exchange reaction of a ZnAl–NO3NO3–LDH/PAO/Al precursor film with the sodium salt of CF3AZO-CF3AZO- anions under mild conditions. The hybrid LDH film was characterized by scanning electron microscopy, powder X-ray diffraction and Fourier transform infrared spectroscopy. TG–DTA, UV–visible spectroscopy and CIE 1976 L*a*b*L*a*b* color difference (ΔE)(ΔE) tests indicated that the intercalated ZnAl–CF3AZOCF3AZO–LDH showed enhanced thermo-stability and photo-stability compared to the pristine CF3AZOCF3AZO salt. Irradiation with UV light led to a switch in wettability of the film from superhydrophobic to hydrophilic and this process could be reversed by subsequent irradiation with visible light.