Measurements of anisotropic surface properties of liquid films of azobenzene derivatives

For imparting anisotropy to the thermophysical properties of solution surfaces, we synthesized an aromatic azobenzene compound with a substituent group including fluorine atoms. We dissolved the synthesized compound in methyl ethyl ketone, and then used a newly developed laser surface light scattering apparatus to investigate the changes in the properties of the liquid film surface when exposed to ultraviolet (UV) radiation (365 nm). The results showed that surface tension increased only when the UV radiation was incident in a direction parallel to the plane of polarization of the measurement laser. In addition, alternate exposure to UV radiation (365 nm) and visible light (435 nm) caused the surface tension to increase and decrease, respectively. It is thought that this is because photoisomerization and anisotropy alignments of the azobenzene compounds occurring on the dissolution surface due to exposure to UV radiation are detected as signal changes in the scattered light. From these results, we found that the measurement method employing the newly developed laser surface light scattering apparatus can be useful as a new evaluation tool for measuring the anisotropy of molecules adsorbed in solution state on a liquid film surface.