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Modern automotive engines operate at higher power densities than ever before, driving a need for new lubricant additives capable of reducing friction and wear further than ever before while not poisoning the catalytic converter. Reported in this paper is a new class of molecular friction modifier (FM), represented by 1,4,7,10-tetradodecyl-1,4,7,10-tetraazacyclododecane (1a), designed to employ thermally stable, sulfur- and phosphorus-free alkyl-substituted nitrogen heterocycles with multiple nitrogen centers per molecule. The multiple nitrogen centers enable cooperative binding to a surface which provides strong surface adsorption and lubricant film durability in the boundary lubrication (BL) regime. A 1 wt % loading of the cyclen FM 1a in Group III base oil exhibits strong surface adsorption, leading to excellent reductions in friction (70%) and wear (95%) versus the pure Group III oil across a wide temperature range. The lubricant with the new FM additive also outperforms two commercially available noncyclic amine-based FMs and a fully formulated commercial 5W30 motor oil.

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A major challenge in lubrication technology is to enhance lubricant performance at extreme temperatures that exceed conventional engine oil thermal degradation limits. Soft noble metals such as silver have low reactivity and shear strength, which make them ideal solid lubricants for wear protection and friction reduction between contacting surfaces at high temperatures. However, achieving adequate dispersion in engine lubricants and metallic silver deposition over predetermined temperatures ranges presents a significant chemical challenge. Here we report the synthesis, characterization, and tribological implementation of the trimeric silver pyrazolate complex, [Ag(3,5-dimethyl-4-n-hexyl-pyrazolate)]3 (1). This complex is oil-soluble and undergoes clean thermolysis at ∼310 °C to deposit lubricious, protective metallic silver particles on metal/metal oxide surfaces. Temperature-controlled tribometer tests show that greater than 1 wt % loading of 1 reduces wear by 60% in PAO4, a poly-α-olefin lubricant base fluid, and by 70% in a commercial fully formulated 15W40 motor oil (FF oil). This silver-organic complex also imparts sufficient friction reduction so that the tribological transition from oil as the primary lubricant through its thermal degradation, to 1 as the primary lubricant, is experimentally undetectable.

We recently reported a new molecular heterocyclic friction modifier (FM) that exhibits excellent friction and wear reduction in the boundary lubrication regime. This paper explores the mechanisms by which friction reduction occurs with heterocyclic alkyl–cyclen FM molecules. We find that these chelating molecules adsorb onto (oxidized) steel surfaces far more tenaciously than conventional FMs such as simple alkylamines. Molecular dynamics simulations argue that the surface coverage of our heterocyclic FM molecules remains close to 100% even at 200 °C. This thermal stability allows the FMs to firmly anchor to the surface, allowing the hydrocarbon chains of the molecules to interact and trap base oil lubricant molecules. This results in thicker boundary film thickness compared with conventional FMs, as shown by optical interferometry measurements.

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The quest for improved engine performance and reduced emissions drives the design of increasingly sophisticated lubrication technologies. Lubricating oils and greases are engineered to function over a broad range of temperatures and loading conditions. Modern engines operate at higher temperatures, speeds and pressures than previous engines, and therefore require lubricants capable of handling harsher conditions. Reliable performance in extreme conditions is also necessary in emergency and combat situations. Thus, a major challenge for next-generation lubrication technology is to improve performance at extreme temperatures exceeding the thermal degradation limits of conventional engine oils.In automotive engines, the surface temperature of critical tribological components can easily reach 200°C, while asperity contacts can generate ‘flash temperatures’ up to 1000°C. These extreme pressures and temperatures in the contact zones can lead to plastic deformation, wear away mating surfaces, and catalyze chemical reactions which damage the surfaces and lubricant. Tests carried out on PAO4 and 15W40 motor oils show that they decompose at 275°C, irreversibly losing viscosity and generating oil-insoluble acids and salts that corrode surfaces and form sludges.Surface coatings, such as diamond-like carbon, and texturing can be used to reduce friction at temperatures which lead to motor oil thermal degradation. However, such treatments are costly for large components, and these coatings cannot be replenished without dismantling the treated machinery. Soft metal ductility can also be utilized in lubrication. The low shear-strengths of metallic films can form smooth “glaze layers” on tribosurfaces which lubricate sliding contact. Noble metals have oxidative stability, enabling lubricious performance at extreme temperatures. Silver-coated contact surfaces exhibit reduced friction and wear from 25–750°C. However, a method is required to dissolve metallic silver precursors in base oil for deposition at high temperatures.Silver nanoparticles are known to increase surface fatigue life, decrease friction, and wear, and work synergistically with other lubricant additives. However, silver nanoparticles are expensive, difficult to suspend in nonpolar media, and typically require a surfactant to prevent agglomeration. An alternative, described here, is to use a silver-containing molecular precursor. Organic ligands impart solubility to silver atoms and control the organosilver complex decomposition temperature to deposit silver only when and where it is needed. Controlled silver deposition is arguably more economical than full protective coatings. Also, a lubricant additive can be replenished during oil changes to provide more lubricious silver to high asperity engine contact regions. We report here the synthesis, characterization, and tribological implementation of a silver-pyrazole complex, silver 3,5-dimethyl-4-n-hexyl-pyrazolate (HPzAg)3. This complex is oil-soluble and undergoes clean thermolysis at ∼310°C to deposit lubricious, protective metallic silver on mechanical surfaces. Temperature controlled tribometer tests show that an optimized 2.5 wt% (HPzAg)3 loading reduces wear by 60% in PAO4 (poly-α-olefin lubricant) and 70% in a commercial fully-formulated motor oil (military grade 15W40). This organosilver complex also imparts sufficient friction reduction that the tribological transition from oil as the primary lubricant through its thermal degradation, to (HPzAg)3 as the primary lubricant, is experimentally undetectable.

High-throughput (HTP) research is becoming more widely utilized due to its advantages in rapid screening of large parameter space. When HTP is used for reaction screening, often only the end products are analyzed by off-line techniques, leaving behind valuable process information. Information-rich spectroscopy tools have remained under-utilized in HTP workflow. In this study near-infrared (NIR) hyperspectral imaging (HSI) is demonstrated to be a versatile and accurate tool that can simultaneously monitor multiple reactions, opening up future opportunities to maximize information extraction from such HTP reaction screening experiments. Model urethane reactions are used here to demonstrate the concept, and the general approach can be widely applied to any reactions involving functional groups changes with NIR spectral changes. The fast speed and accurate chemical information made possible by NIR HSI are expected be another important addition to the toolkit of HTP research.