Thin film lubrication experimental study

In the past decade, effects of an EEF on the properties of lubrication and wear have attracted significant attention. Many experimental results indicate that the friction coefficient changes with the intensity of the EEF on tribo-pairs. These phenomena are thought to be that the EEF can enhance the electrochemical reaction between lubricants and the surfaces of tribo-pairs, change the tropism of polar lubricant molecules, or help the formation of ordered lubricant molecular layers [51,73-77]. An instrument for measuring lubricant film thickness with a technique of the relative optical interference intensity (ROII) has been developed by Luo et al. [4,48,51,78] to capture such real-time interference fringes and to study the phenomenon when an EEF is applied, which is helpful to the understanding of the mechanism of thin film lubrication under the action of the EEF. 

Several examples of experimental approaches to thin-film lubrication have been reported [3]. It is important in examining these techniques to make the distinction between methods that are used to determine lubricant film thickness under hydrodynamic or elastohydrodynamic conditions (e.g., optical interference, electrical capacitance, or x-ray transmission), and methods that are used to determine the occurrence or frequency of contact. As we will see later, most experimental studies of synovial joint lubrication have focused on friction measurements, using the information to determine the lubrication regime involved this approach can be misleading. 

In this section we present fundamental scientific tools as well as potential applications relevant to the emerging field of nanotechnology. For instance, understanding the behavior of molecularly thin lubricant films via experimental and theoretical study of the physicochemical properties of ultrathin... 

If the idealized concept of fluid film failure proposed above is to have any significance in the world of experimental mechanics and engineering, we must find a basis for its validity and utility. The study of fluid film failure in a practical sense then becomes the study of the behavior of the boundary surfaces of the solids and of the intervening fluid lubricant as the thickness of the lubricant film approaches zero. An important aspect is the reliability of the measurement technique for very thin films. We must be careful not to think of fluid film failure as rupture or breakdown by exceeding the intrinsic strength of the lubricant material. Bulk liquid films do not behave in that way. We know by hydrodynamic theory that the pressure a film of fluid is able to... 

COF for oxide-based tribo-systems was observed when adding PLL-g-PEG to aqueous buffer solution. The present study is a continuation of this work, focusing on the architectural parameters of the PLL-g-PEG copolymer and its influence on the macroscopic lubrication properties. The architectural parameters investigated in this work include side-chain (PEG) length, Lys/ PEG grafting ratio and backbone (PLL) length. The experimental techniques employed are ultra-thin-film interferometry, the mini-traction machine (MTM), and pin-on-disk tribometry. 

It is therefore necessary to determine the slurry film thickness under the various sawing conditions. The hydrodynamic behavior of slurry films has been studied in lubrication or polishing processes, where many fundamental aspects have been derived from experimental and theoretical results [15, 16]. An important aspect is that the wire, and to some extent the crystal, can deform elastically in response to the slurry pressure. Considering that the wires are thin and long it is very likely that mainly the elastic response of the wire has to be considered when the slurry transport is analyzed. In the following the main aspects of the problem are derived from a one-dimensional treatment of the hydrodynamic slurry transport below a flexible wire. 

Atomic-level lubrication has been investigated both experimentally and theoretically. Experimental techniques, such as the surface force apparatus (SFA), have been used to study thin molecular films. It has been shown that behaviours of thin films, of a few molecular diameters thick, are generally quite different fi-om their... 

The mechanisms of static friction and stick-slip motion, as discussed in the last section, are supposed to be a good description of dry friction. Another case, perhaps more general in engineering practices, to be addressed in this section is lubricated sliding where liquid lubricant, consisting of a few molecule layers, is confined between two solid walls. Both experimental and theoretical studies indicate, as we have discussed in Chapter 5, that there are substantial changes in rheology of the confined lubricant, and the liquid may transit practically to a solid-like state when film thickness becomes molecularly thin [32,33]. 

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