Friction-force measurements between a silica sphere and a titanium dioxide
wafer in electrolyte solutions were made using an atomic force microscope.
The effect of electrical double-layer interactions on the adhesion and the
friction force were Investigated as a function of pH. In contrast to taking
friction measurements in air, conducting the study in aqueous solution has
allowed the surface separation, adhesion, and applied force to be controll
ed independently. Friction was found to be dependent only on the intrinsic
force. Friction was seen to be independent of pH. When a farce law fitted t
o the measured data was used, the separation as a function of intrinsic for
ce was likewise found by theoretical calculations to be independent of pH.
It was concluded that friction was solely dependent on separation and that
the effect of applied force and electrical double-layer interactions served
merely to change the separation. In addition, it was proposed that a singl
e layer of unbound water molecules effectively lubricated the surfaces.