Studying the Tribological Properties of n-alkanes Monolayer Films on Atomic Flat Surface of Gold

1Vasko, AA
1Marchenko, AA
1Naumovets, AG
1Braun, OM
1Institute of Physics of the NAS of Ukraine
Sci. innov. 2019, 15(4):62-68
Section: Research and Engineering Innovative Projects of the National Academy of Sciences of Ukraine
Language: English
Introduction. The establishment of regularities of the microcontact interaction in the friction interface formed by two moving bodies is an important step towards the creation of new classes of materials with predefined physicochemical properties. The relative motion of interacting surfaces inevitably results in wearing contact areas (microcontacts) of these surfaces, that is, it leads to the formation of pieces that are caused by destruction of more elastic material.
Problem Statement. The destruction of the interface decreases significantly by applying lubricant films to the contact area. In the case of dry friction (no lubricant), the description of the contact area is a practically solved problem (the Hertz and the Johnson-Kendal-Roberts contact theories), while the presence of lubricant complicates it, i.e., one should consider the rheological component of friction and the interaction of interfaces. In addition, the overwhelming majority of tribological studies were carried out using imperfect (rough) surfaces and lubricant films with uncertain component composition, thickness, and structure.
Purpose. To establish the influence of the structure of self-assembling n-alkanes monolayers on their tribological properties in the frictional interface.
Materials and Methods. The atomically flat surface of gold and one-component monolayer films of n-alkanes 
(CnH2n+2, n = 14, 16, 48, 50, 60) are used as materials. The scanning tunneling microscopy method is used to establish the structure of self-assembled monolayers on the gold surface as well as to control stability of monolayers before and after the tribological measurements. The kinetic coefficient of friction μko of interfaces have been studied using a magnetic levitation tribometer.
Results. The nonmonotonic dependence of kinetic friction coefficient μko on the length of n-alkane molecule has been experimentally established.
Conclusions. The kinetic friction coefficient μko has been established to abnormally decrease for the n-alkanes with “magic length” (n times 16).
Keywords: atomically flat surfaces, coefficient of friction, friction force, monolayer films of n-alkanes