Tribochemical synthesis of nano-lubricant films from adsorbed molecules at sliding solid interface: Tribo-polymers from α-pinene, pinane, and n-decane

Abstract

The mechanochemical reactions of adsorbed molecules at sliding interfaces were studied for αpinene (C 10 H 16), pinane (C 10 H 18), and n-decane (C 10 H 22) on a stainless steel substrate surface. During vapor phase lubrication, molecules adsorbed at the sliding interface could be activated by mechanical shear. Under the equilibrium adsorption condition of these molecules, the friction coefficient of sliding steel surfaces was about 0.2 and a polymeric film was tribochemically produced. The synthesis yield of α-pinene tribo-polymers was about twice as much as pinane tribo-polymers. In contrast to these strained bicyclic hydrocarbons, n-decane showed much weaker activity for tribo-polymerization at the same mechanical shear condition. These results suggested that the mechanical shear at tribological interfaces could induce the opening of the strained ring structure of -pinene and pinane, which leads to polymerization of adsorbed molecules at the sliding track. On a stainless steel surface, such polymerization reactions of adsorbed molecules do not occur under typical surface reaction conditions. The mechanical properties and boundary lubrication efficiency of the produced tribo-polymer films are discussed.

Mechanochemical Reactions of Adsorbates at Tribological Interfaces: Tribopolymerizations of Allyl Alcohol Coadsorbed with Water on Silicon Oxide

“…Chemical reactions can occur not only by thermal, photochemical, and electrochemical activations but also by mechanical activations; mechanically driven reactions are the subject of mechanochemistry. − In particular, chemical reactions induced by interfacial shear or friction at tribological systems are called tribochemistry. − Well-known industrial examples of tribochemical reactions are the production of antiwear films by zinc di­alkyl­di­thio­phosphate (often referred to as ZDDP) and the formation of a friction-modifier layer by molybdenum di­thio­carbamate (MoDTC); both are widely used additives in automobile engine oils. − The formation of such surface films (often called tribofilms) is highly dependent on interfacial shear actions. − Without shear, tribofilms do not form efficiently. Even if a surface film is formed by the same chemicals through thermal reactions, the composition and structure of the film formed without shear are different from those of tribofilms, and its performance is inferior to that of tribofilms. − To improve the performance of such tribofilms or design better additives that can outperform the currently used additive chemicals, it is critical to understand the mechanisms of tribochemical reactions at the molecular level. However, the current mechanistic understanding of tribochemical reactions occurring in practical applications is quite rudimentary because of the complexity of individual steps involved in such reactions and/or the difficulty of detailed characterizations of tribochemical reaction products at the molecular level.…”

Lithium anode stable in air for low-cost fabrication of a dendrite-free lithium battery

“…Figure 4d, e gives the force curves as a function of tip–surface distance during the indentation loading and unloading cycle; the slopes of the load and unload curves are attributed to the stiffness of the material being probed with the AFM tip. The measured largest negative force is the adhesion force between the probed surface and tip 33 . In Fig.…”

Tribological behaviour of graphene oxide sheets as lubricating additives in bio-oil

“…This can be explained by the fact that the GO sheets are easier to aggregate at high concentration (Yang et al, 2015;Giuri et al, 2017), which restricts the uniform adsorption of GO sheets on the frictional interfaces. On the other hand, lower GO sheets concentration is hard to form a complete adsorbed film on the sliding surfaces (He et al, 2016), which is also adverse to the lubrication.…”