| Abstract
| - The friction and lateral stiffness of the contact between an atomic force microscopy (AFM) probe tip and anatomically flat dolomite (104) surface were investigated in contact with two aqueous solutions that were in equilibriumand supersaturated with respect to dolomite, respectively. The two aqueous solutions yielded negligible differencesin friction at the native dolomite−water interface. However, the growth of a Ca-rich film from the supersaturatedsolution, revealed by X-ray reflectivity measurements, altered the probe−dolomite contact region sufficiently toobserve distinct friction forces on the native dolomite and the film-covered surface regions. Quantitative friction−loadrelationships demonstrated three physically distinct load regimes for applied loads up to 200 nN. Similar friction forceswere observed on both surfaces below 50 nN load and above 100 nN load. The friction forces on the two surfacesdiverged at intermediate loads. Quantitative measurements of dynamic friction forces at low load were consistent withthe estimated energy necessary to dehydrate the surface ions, whereas differences in mechanical properties of theCa-rich film and dolomite surfaces were evidently important above 50 nN load. Attempts to fit the quantitativestiffness−load data using a Hertzian contact mechanical model based on bulk material properties yielded physicallyunrealistic fitting coefficients, suggesting that the interfacial contact region must be explicitly considered in describingthe static and dynamic contact mechanics of this and similar systems.
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