Evaluation of interfacial water on super-hydrophilic surface by THz-TDS

Transmission-type THz-TDS was applied to characterize water on super-hydrophilic surface of anatase-TiO₂ layer fabricated by plasma-assisted deposition. Absorption coefficient of water with the thickness of 300 mm on the layer was in good agreement to that of free water before the surface was converted to the super-hydrophilicity but decreased on the super-hydrophilic surface after UV-irradiation. The complex dielectric constant was fitted by double Debye-model and could be explained by a model of double water layers consisting of free water and interfacial water near the super-hydrophilic surface after UV-irradiation. The slow relaxation time of 37 ps in the interfacial layer with the thickness of 45 μm was significantly large comparing to the value of 7.7 ps in free water.