Title:
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Investigations of the frictional behaviour of
nanotextured surfaces by friction force microscopy
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Friction is omnipresent in our daily life, and although this phenomenon has been studied for centuries,
the fundamental understanding on tribological processes as a whole is still lacking. Reducing friction is
beneficial in many applications, from mediating wear to improving the life span of devices, hence
improving our knowledge of the parameters affecting frictional forces is of paramount importance. In
particular, the miniaturisation of modern devices implies that their reliability and durability become
friction limited.
Recent advances in the fabrication of nanostructured surfaces with tuneable topographic properties,
along with advances in metrological tools such as the atomic force microscope (AFM), now provide the
means to systematically study friction on well-defined nanostructured surfaces. This research project is
focused on the lubricated and un lubricated frictional behaviour of nanotextured surfaces using the AFM
with conventional and colloidal probes. The frictional properties of nanotextured surfaces bearing
aluminium oxide nanodomes and zinc oxide nanorods of varying topographic properties in air, as well as
the frictional properties in aqueous solutions of ionic and nonionic surfactants on flat and textured
surfaces of titanium oxide, are reported.
The results show that for the nanodomed-textured surfaces, the ancient Amontons laws of dry friction
are obeyed; however, the friction coefficient was insufficient to fully characterise the frictional behaviour
of such nanotextured surfaces. Pronounced stick-slip frictional characteristics were observed, with the
amplitude of the stick-slip varying linearly with the applied load. On nanorod-textured surfaces, the
friction-applied load linear relationship was however lost, due to the bending contributions of the rods to
the lateral force experienced by the probe. Finally, the results obtained on flat and pillar-textured
titanium oxide surfaces showed that ionic surfactants could mediate effective boundary lubrication with
the existence of two frictional regimes, due to load- and shear-induced structural changes in the
nanofilms of the adsorbed surfactant molecules.
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