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Development of low friction surface materials matched with low friction lubricants is an important route to improving engine efficiency and reducing emissions. Diamond-like carbon (DLC) is a material of interest because it combines the durability of diamond with the low friction properties of graphite. Consequently, various forms of DLC have been studied as durable, low friction surface coatings. At the same time, friction modifiers (FMs) are often used in engine lubricants to produce low friction surface layers. Molybdenum-based friction modifiers are commonly used additives that mechanochemically decompose to cover surfaces with MoS2, a solid lubricant. FMs can also reduce friction on DLC surfaces. However, molybdenum can be harmful to DLC and cause rapid degradation and breakthrough of the DLC surface layer. We have found that the wear debit of molybdenum FMs trends with surface affinity of the additive. The adsorption isotherms of 4 Mo-based FMs on boron-doped diamond-like carbon (BDLC) were measured with a quartz crystal microbalance (QCM). The strongest adsorbate, Mo dithiophosphate (MoDTP), which also forms the thickest film, protects the BDLC surface enabling low friction while keeping wear low. Theoretical predictions based on molecular dynamics simulations combined with molecular-thermodynamic theory (MD-MTT) show that adsorption of MoDTP on BDLC deviates significantly from Langmuir behavior and free energy of adsorption for the first monolayer is significantly more negative than the multilayer adsorption free energy observed experimentally. The relationship between wear and adsorption behavior is consistent with experimental observations in the literature. These results also suggest that additive performance in a fully formulated lubricant is related to fundamental adsorption properties measured on the neat additive.

Polyoxin-B-treated and untreated (control) hypae of Alternaria kikuchiana Tanaka were first degraded with 2N NaOH, 1N H2SO4, and digestive enzymes, and then morphological alterations of the cell walls were investigated by cytochemical methods and electron microscopy. A pronounced difference between control and treated hyphae was seen after sequential treatment with NaOH-H2SO4-NaOH. Inner wall layers of controls were transformed into numerous microfibrils; these were identified, in turn, by chitinase and Lytic enzyme digestions as chitin and β-1, 3-glucan intermixed with protein. But these same treatments failed to structurally degrade the walls of polyoxin-treated hyphae. In the controls, only the thin outer wall layer showed any resistance to the treatment, but in polyoxin-treated hyphae the entire cell wall, including septae and walls of intracellular hypha, was resistant to a sequence of the degradative treatments. Cytochemical tests revealed that both control and polyoxin-treated hyphae, which originally contained chitin, no longer responded positively to tests for chitin after chitinase or HCl treatment following treatment with the NaOH-H2SO4-NaOH sequence. This study suggests two possibilities i) cell walls, especially inner wall layers, of control and polyoxin-treated hyphae may have different structural constituents, and ii) melanin-like pigments in inner cell walls may be associated with the resistance of polyoxin-treated hyphae to lysis by digestive enzymes.