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 (CF(3)AZO(-)), 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-NO3-LDH/PAO/Al precursor film with the sodium salt of CF(3)AZO(-) 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* color difference (Delta E) tests indicated that the intercalated ZnAl-CF(3)AZO-LDH showed enhanced thermo-stability and photo-stability compared to the pristine CF(3)AZO 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. (C) 2009 Elsevier Ltd. All rights reserved.