We have synthesized and conducted studies on two self-assembled monolayers which have an oxyaniline tail group that is tethered to a gold surface via an alkanethiol chain. Reflection-absorption infrared spectroscopy (RAIRS), electrochemical, and contact angle measurements were performed on pristine 2-(6mercaptohexan-1-oxy)aniline (AnC6SH) and 2-(7-mercaptoheptan-1-oxy)aniline (AnC7SH) monolayers on planar Au surfaces. The pristine monolayers were electrochemically oxidized in 1 M H2SO4, and the resulting voltammetry was compared to that of dimeric model compounds and electrochemically deposited poly(o-phenetidine) films on Au electrodes. RAIRS and electrochemical data reveal that electrochemical oxidation of AnC6SH and AnC7SH monolayers on Au results in the formation of surface-confined poly-(aniline) as well as aniline dimers and hydrolyzed aniline dimers.

The stability and electrochemical properties in nonaqueous media of self-assembled alkanethiol monolayers containing an alkoxyaniline tail group tethered to a gold surface via a hexyl or heptyl chain were investigated. It was previously found that upon electrochemical oxidation in 1 M H2SO4, 2-(6-mercaptohexan-1-oxy)aniline (AnC6SH) and 2-(7-mercaptoheptan-1-oxy)aniline (AnC7SH) monolayers on Au give rise to surface-confined dimeric and oligomeric/polymeric anilines as well as surface-confined hydrolyzed aniline dimer. In the study at hand, AnC6SH/Au and AnC7SH/Au were electrochemically oxidized in 0.1 M LiClO4/CH3CN to discourage the formation of surface-confined hydrolyzed aniline dimer. The resulting voltammetry was compared to that observed for monolayers oxidized in 1 M H2SO4 and that of dimeric model compounds in 0.1 M LiClO4/CH3CN. Reflection-absorption infrared spectroscopy and electrochemical data reveal that upon oxidation in a nonaqueous electrolyte both AnC6SH/Au and AnC7SH/ Au yield head-to-tail coupled, surface-confined oligomers and no detectable amounts of hydrolyzed products.

Performance additives are found in all quality lubricants or the fluid would be sold as a basestock. These additives have many functions, some of which include corrosion protection, antioxidant, antiwear, acid neutralizations, dispersancy, detergency, and antifoam protection. The type of additives formulated in the fluid is a function or appetite of the lubricant's application. Nearly all lubricants are formulated to minimize the bad properties and improve the good properties—thus promoting smooth, reliable operation of the equipment. An important part of that operation is controlling and dissipating heat from the equipment. Temperature is an important, sometimes uncontrolled property of the equipment's operation that can lead to a number of fluid reactions both beneficial and damaging to the lubricant's formulation and the lubrication system. Unfortunately, the thermal stability of many of the lubricant additives being used today is overlooked or not well understood. There are several analytical methods available within the ASTM literature designed to reveal the thermochemical behavior of materials. However, there is little data available using the methods for these additives. Two main thermoanalytical techniques that can be used to investigate the thermal stability of lubricant additives are thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The procedures that describe these property measurements within ASTM are standards such as E1131, E1641, and E2550, which use the TGA technique for assessing the thermal stability and compositional analysis of most any hydrocarbon materials. The DSC standards such as E487, E537, E1858, E2009, and E2046 can be used to study in‐service lubricant lifetimes by evaluating lubricant stability and oxidation properties. In this study, an array of lubricant additives was tested against these ASTM standards to understand the additive's thermal stability and chemical behavior toward extreme temperature excursions. The results of this testing program are reported.

Varnish formation is a major problem that leads to costly lubricant-related mechanical failure of machinery equipment. Varnish is typically regarded as the organic insoluble matter within a lubricant that can plug filters to cause flow issues or coat equipment parts, forming a contamination layer. Varnish formation within equipment has been attributed to several issues, including oxidation and thermal decomposition within the fluid, electrostatic spark discharge, excessive operational temperatures, contamination ingress, and additive decomposition. In some recent case studies of gas turbine bearings and servo-valve equipment, the formation of a surface varnish coating having high concentrations of phosphate chemistries contributed to the root cause of the equipment failure. A common source of phosphorus in many lubricants is the phosphate antiwear additives that function by actively forming thin surface films (in some cases monolayer) to supply the antiwear or anticorrosion protection. It has been seen that at exceedingly high surface levels of the additive chemistry, the additive itself will deposit acting as the varnish—leading to the question of why/how it is forming in this manner. The thermal stability of the in-service fluid and its antiwear additive were studied herein to understand the thermal-oxidative reaction pathways that could lead to a root cause of the varnish formation within a lubricant. The thermal stress of new and in-service lubricants was investigated using thermal stability and oxidation standards ASTM E2550 and ASTM E1858 to produce a varnish. Qualitative analysis of the varnish layers was then performed by ASTM E1252 using infrared spectroscopy, and the in-service lubricant chemistry was evaluated using ASTM D7418.

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