Triboattraction: Friction under Negative Load

When a square single-crystal diamond slider with a smooth flat surface is placed in contact with a rotating smooth surface of amorphous carbon, we observe the development of an attractive force. The force is such that even when the load applied to the slider is made negative (i.e., the slider is pulled away from the surface), it still remains in physical contact with the rotating surface, and its frictional force can be measured. This attractive force is maintained so long as the slider is rubbing against the rotating disk but ceases when the rotation is stopped. Experiments to investigate this triboattractive force indicate that it is due to electric charge generated by triboelectricity. The present observation is compared to previous reports of friction under negative load. © 1990, American Chemical Society. All rights reserved.