Reversible wettability of photoresponsive fluorine-containing azobenzene polymer in Langmuir-Blodgett films

A polymer containing 3'-[trifluoromethyl-4,3'-dibenzoazo] dyes in the side chains has been synthesized, and a monolayer of this polymer has been transferred onto solid substrate by the Langmuir-Blodgett (LB) technique. The reversible processes of photoisomerization of the LB films induced by light are observed by UV-vis absorption spectra, in situ atomic force microscopy, and friction force microscopy. In addition, the physisorbed monolayers of the monomer of the polymer at liquid/solid interface are investigated by scanning tunneling microscopy. The films of the polymer show the reversible change of morphological and friction force responses under alternate UV(365 +/- 10 nm) and visible (436 +/- 10 nm) irradiation. The films also undergo reversible wettability changes with UV and visible light irradiation, which are directly confirmed by contact angle measurement. The largest photoinduced change of contact angle is 11 +/- 1 degrees. The larger value of the contact angles measured corresponds to films mainly composed of the trans isomers of the molecules. Evidence shows that the photoinduced surface energy changes have an important influence on the wettability changes.