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A Quantitative Study of Interaction Forces and Friction in Aqueous Colloidal Systems

Summary: A Quantitative Study of Interaction Forces and Friction in
Aqueous Colloidal Systems
Adam Feiler, Ian Larson, Paul Jenkins, and Phil Attard*
Ian Wark Research Institute, University of South Australia, Mawson Lakes,
Adelaide SA 5095, Australia
Received June 23, 2000. In Final Form: September 25, 2000
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 controlled independently. Friction was found to be dependent only on the intrinsic
force. Friction was seen to be independent of pH. When a force law fitted to the measured data was used,
the separation as a function of intrinsic force 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 single layer of unbound water molecules effectively lubricated the surfaces.
In recent years direct measurement of frictional force
at the molecular scale has become possible, in particular
with the use of the atomic force microscope (AFM)1


Source: Attard, Phil - School of Chemistry, University of Sydney


Collections: Chemistry