The role of adsorbed water on TiO2 particles in the electrorheological effect

TiO2 particles prepared by the hydrolysis of titanium butoxide adsorb water molecules with different adsorption energies. The electrorheological (ER) fluid composed of TiO2 particles behaves as the polar-molecule giant electrorheological (GER) fluid at 25°C even after thermal treatment at 75°C. After thermal treatment at 125°C and 175°C, the water molecules with low adsorption energy are removed and the ER fluid behaves as traditional ER fluid at 25°C. However, at 175°C, the ER fluid treated at 175°C behaves as a polar-molecule GER fluid when the external electric field is larger than 2 kV/mm. These results show that the water molecules with low adsorption energy act as polar molecules responsible for the GER effect and, with the help of thermal energy, water molecules with high adsorption energy can work as those with low adsorption energy, resulting in the GER effect.