Recently, titanium dioxide (TiO_2) attracts a great deal of attention as a photocatalyst. When ultraviolet right is irradiated, ultra-hydrophile property, that is the contact angle under 5 degrees between water and substrate, occurred. In this study, the friction property of titanium dioxide photocatalyst under ultraviolet irradiation was investigated. TiO_2 coated on a glass plane was rubbed against a glass lens in dry sliding and in water lubrication under ultraviolet irradiation. The coefficient of friction between TiO_2 coat and glass lens with water without ultraviolet irradiation was higher than that of dry sliding. The coefficient of friction at water lubrication with ultraviolet irradiation became lower than that of without ultraviolet irradiation and decreased with increasing the irradiation time. The reduction rate deduced as the irradiation time increased. The influence of ultraviolet irradiation continued for tens hours since the coefficient of friction showed a slight decrease.

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The friction of silica-filled styrene butadiene rubber (SBR) and carbon black-filled SBR with different glass transition temperature (T_g) under dry sliding and lubrication of water and silicon oil was investigated with ball-on-plate apparatus at normal load of 0.98N and sliding speed from 0.1mm/s to 1mm/s. A total reflection prism was used as the mating surface so as to study the relationships between the contact area and the coefficient of friction. It was found that the coefficient of friction of silica-filled SBR was higher than that of carbon black-filled SBR both in dry and lubricated sliding. The coefficient of friction of the SBR specimen with higher T_g was high, regardless of the filler. The coefficient of friction was the highest at dry sliding and was the smallest at water lubricated sliding. The contact area was the highest at water lubricated sliding and was the smallest at dry sliding.

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