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Yingxi Zhu Hiroko Ohtani Michael L. Greenfield Marina Ruths Steve Granick 《Tribology Letters》2003,15(2):127-134
The molecular-level function of model and commercial friction modifier additives in lubricants of the type used at the wet clutch interface in automatic transmissions has been studied using a surface forces apparatus (SFA) modified for oscillatory shear. The nanorheological properties of tetradecane with and without a model friction modifier additive (1-hexadecylamine) were examined in the boundary lubrication regime and compared to a fully-formulated automatic transmission fluid (ATF). 1-Hexadecylamine adsorbed as a single layer on the sliding surfaces, reduced the static frictional force and the limiting shear stress, and eliminated the stick–slip transition that exists in pure tetradecane. The ATF, which contains commercial-grade friction modifiers, showed nanorheological properties similar to those observed for tetradecane containing 0.1–0.2 wt% 1-hexadecylamine. 相似文献
2.
The dynamic shear properties of molecularly-thin films of unfunctionalized and end-functionalized (telechelic) Fomblin-Z perfluoropolyalkylether
(PFPAE) melts with number-average molecular weight M
n≈ 3000−4000 g,mol-1 have been studied at shear rates of 10-2−105 s-1 at normal pressures of 1 and 3 MPa. The shear responses are compared to measurements on end-functionalized polymers of the
same chemical composition but lower molecular weight, M
n≈ 2000 g,mol-1. The predominantly elastic response and high shear moduli of the confined film of unfunctionalized polymer, Fomblin Z03,
suggest that it forms a structure likely to solidify already at low pressure. Its lubricating properties are less favorable
than the ones found for hydroxyl- (DOL) and piperonyl-terminated Fomblin-Z (AM2001, AM3001), where associated molecules form
a structure less prone to solidification under confinement. The thickness of the compressed films of the end-functionalized
polymers increased more strongly with molecular weight than as M
n
0.5
. The shear moduli were found to be larger, the higher the molecular weight, indicating slower relaxations. At a normal pressure
of 3 MPa, these films solidified and displayed stick–slip as seen already at 1 MPa in the Z03 film. The limiting shear stress
of the unfunctionalized Z03, σ > 3 MPa, exceeded by an order of magnitude the limiting shear stress of all of the end-functionalized
polymers. The limiting shear stress of the hydroxyl-terminated polymer was larger than that of the piperonyl-terminated polymer.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
Ruths Marina Ohtani Hiroko Greenfield Michael L. Granick Steve 《Tribology Letters》1999,6(3-4):207-214
Dilute solutions of two polar end‐functionalized linear alkanes (1‐hexadecylamine and palmitic acid), each dissolved in tetradecane,
were confined between two mica surfaces and investigated using a surface forces apparatus modified to study shear nanorheology.
These two solutions showed similar nanorheological properties that differed from those observed for pure n‐alkanes. In static measurements, a “hard wall”, rather than an oscillatory force, was observed as a function of film thickness.
The polar alkane component formed a weakly adsorbed single layer at each mica surface, disrupting the layered structures found
in neat n‐tetradecane. In dynamic experiments at low shear amplitude, the storage modulus G' exceeded the loss modulus G" at low frequencies;
above some characteristic frequencies G' increased such that g' ≈ G", indicating significantly more energy loss through viscous
modes at higher frequency. When the amplitude was varied at fixed frequency, no stick–slip was observed and the limiting value
of the shear stress at high effective shear rate was an order of magnitude less than for unfunctionalized n‐alkanes at similar loads. Together, these results show that the addition of a small amount of polar alkane component, by
disrupting the layered structures that would have been formed in the neat n‐alkane, is effective in suppressing static friction and reducing kinetic friction in the boundary lubrication regime.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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