Proceedings of SerbiaTrib '13

Serbian TribologySocietySERBIATRIB ‘1313 th International Conference onTribologyKragujevac, Serbia, 15 – 17 May 2013Faculty of Engineeringin KragujevacDYNAMICS OF SAMS IN BOUNDARY LUBRICATIONJelena Manojlović 11 The Faculty of Mechanical Engineering, University of Niš, Niš, Srbija, jmanojlo@gmail.comAbstract: Surfactant molecules have some properties responsible for a number of remarkable phenomena,such as oriented adsorption of surfactants at surfaces and interfaces. The capability to self-assemble intowell-defined structures is often seen as being more important than their surface activity. When a surfactantsolution is in contact with a solid surface, the surfactant molecules adsorb onto the surface, ideally formingan adsorbed layer of high order, termed as self-assembled monolayer (SAM). Many surface properties areinfluenced by such a film, and therefore, SAMs offer the capability to form ordered organic surface coatings,suitable for various applications, such as wetting or corrosion protection. Due to the flexibility in choosingthe molecular architecture, organic molecules have many interesting applications, such as biosensors, inphotoelectronics, in controlling water adsorption or boundary lubricant coating. This paper focuses oncationic surfactants (quaternary ammonium surfactants), with some unique properties that are not present inother surfactants.Keywords: surfactants, self-assemble, boundary lubrication, nanotechnology.1. INTRODUCTIONA contact between two surfaces is of greatimportance in technology. At the interface of twomaterials, when they are brought together,separated or moved with respect to one another,contact formation, friction, wear or lubrication arethe processes that occur [1]. Friction has long beenthe subject of research. All machined metalsurfaces, as viewed through a microscope, havetheir own roughness, called asperity. Therefore, twosurfaces touch at an extremely small number ofpoints, and their true area of contact is a part oftheir apparent contacting area. In contact of twosurfaces, the number of asperities increases due toplastic deformation of some of them. Theconsequence of this is the appearance of theremoval of material from a surface in bearing underdynamic conditions, defined as wear [2]. In order toreduce wear, lubricants are employed between thesurfaces. Friction, wear and lubrication are thecenter of consideration in many tribological andtechnological problems. Having in mind that acontact occurs in numerous asperities, the researchof two contact surfaces, especially at the molecularlevel and the friction phenomenon at the nanometerscale, is studied by nanotribology, a branch oftribology.In order to categorize the friction propertiesbetween two surfaces, the "Stribeck curve" wasdeveloped. Machine elements may experienceseveral lubrication regimes, including full-film,mixed, and boundary lubrication. These regimesdepend on the properties of a lubricant andoperating conditions. In the case where speeds aretoo low and loads are too high to permitestablishing a hydrodynamic film, or when thedistance between contact surfaces is a fewnanometers or a few molecular layers, we candefine boundary lubrication (fig.1).Figure 1. Boundary lubricationThe boundary films have been the subject ofstudy for decades, since friction and wearphenomena are affected by these ultrathin films.Under friction, the dynamics of lubricants onsurfaces is very important, especially the molecularbehavior of lubricants in boundary lubrication. Thebehavior and dynamics of the boundary films,13 th International Conference on Tribology – Serbiatrib’13 153