EFFECT OF ADSORBED WATER ON THE PHOTOELECTRORHEOLOGY OF TIO2 PARTICLESUSPENSIONS

The photoelectrorheological properties of several types of TiO2 sample s having widely varying surface water contents were examined in order to understand the role of water in the photoelectrorheology of TiO2-ba sed fluids. The particles having low water contents showed an increase in the ER effect upon illumination, which is due to a polarization by photogenerated charges. The diminution in the photoeffect with increa sing water content on the particles is attributed to the partial remov al of photogenerated charges which have been trapped as a result of re actions involving water, adsorbed OH groups and oxygen, e.g. reduction of adsorbed hydroxyl radicals and oxidation of adsorbed superoxide. T he resulting photoelectrophoretic effect is believed to dominate the e lectrorheological force, thus reducing the photoeffect. (C) 1998 Elsev ier Science S.A. All rights reserved.