Among friction modifier lubricant additives, molybdenum dialkyldithiocarbamate (MoDTC) provides excellent friction behavior in boundary lubricated tribocontacts. It is well established that the low friction obtained with MoDTC is as a result of the formation of lattice structure MoS 2 nanosheets. However, the relationship between the molybdenum species quantity, its distribution on the contact surface, and the friction behavior is not yet fully understood. In this work, Raman microscopy and atomic force microscopy (AFM) have been used with the aim of understanding the link between the friction behavior and the MoDTC/ZDDP tribofilm formation and removal. Tribotests were coupled with a collection of ex-situ Raman intensity maps to analyze the MoS 2 tribofilm buildup. Post-test AFM analyses were implemented on the ball wear scar to acquire the average MoDTC/ZDDP tribofilm thickness. In-situ Raman spectra analyses were carried out to detect the MoS 2 tribofilm removal. A good correlation was achieved between the friction coefficient measurements and Raman maps when using a linear relationship between the microscopic friction and the local amount of MoS 2 tribofilm. After a rapid increase, the average MoDTC/ ZDDP tribofilm thickness levels out to a steady state as the friction drop ceases. The removal rate of MoS 2 from tribofilms, obtained at different temperatures, suggests that the MoS 2 tribofilms are much easier to remove from tribocontacts compared to antiwear ZDDP tribofilms. This is the first study that sets out a framework to link MoS 2 amount and coverage to the friction behavior, providing the basis for developing numerical models capable of predicting friction by taking into account tribochemistry processes.

Please cite this article as: Carrión, F.J., Espejo, C., Sanes, J., Bermúdez, M.D., Single-walled carbon nanotubes modified by ionic liquid as antiwear additives of thermoplastics, Composites Science and Technology (2010), doi: 10.1016/j.compscitech.2010 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Nanocomposite films for covering applications were developed. Mechanical, radiometric and ultraviolet stability properties of the films were characterized. Nanocomposites were obtained by incorporating nanoadditives to a thermoplastic polymer matrix by melt-mixing in a corotating twin screw extruder. Three common polymers in cover applications were used as matrix: low-density polyethylene, linear low-density polyethylene and ethylene-butyl acrylate. Three different nanoparticles were used as fillers (2 wt%): titanium dioxide (rutile), silicon oxide and zinc oxide. All nanocomposites were processed in a blown film extrusion line, producing 200 mm thick films. The mechanical properties of the nanocomposite films were found to be slightly different than those of the neat films, whereby the optical and radiothermal properties changed dramatically. Titania nanocomposite containing films had high ultraviolet shielding, however, significantly reduced transparency. Zinc oxide introduced high ultraviolet-shielding capability preserving transparency. High infrared efficiency has been found in silica nanocomposite films, exhibiting efficiency values greater than 79%, and an increment greater than 100% for linear low-density polyethylene and low-density polyethylene nanocomposite films. The extent of ultraviolet degradation of the films was determined by elongation at break tests. Zinc oxide/low-density polyethylene Downloaded from film underwent less degradation than neat low-density polyethylene film after photoaging. Thus, zinc oxide-filled polymer nanocomposite films are suitable for transparent ultraviolet-shielding applications and present low degradation rates. Silica incorporation highly improves polyethylene infrared efficiency, rendering a low-cost high-thermicity transparent film.

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The rheological behavior of 1-ethyl-3-methylimidazolium tosylate (EMIMTsO) and its dispersions with aligned and non-aligned multi-walled carbon nanotubes (MWCNTs) has been studied. Raman spectroscopy analysis has been carried out to characterize the samples. The effects of concentration, type of CNTs and temperature on the viscolelastic behavior of EMIMTsO have been evaluated. Regardless the concentration and type of added CNTs, a non-Newtonian behavior of the fluids has been found under shear stress.The ionic liquid and the EMIMTsO-MWCNTs 1 wt% dispersion showed a temperatureinduced gelation. However, the addition of small concentrations of MWCNTs prevents from the formation of gels.

This work focuses on the tribochemistry of molybdenum dithiocarbamate (MoDTC) oil additive to improve friction behavior of diamond-like-carbon (DLC) coated systems lubricated in boundary regime. Raman microscopy has been used to investigate surface tribolayers formed on coated (hydrogenated a-C:H and non-hydrogenated ta-C) and steel surfaces when lubricated with model lubricants and commercial engine oils. The effect of the additive package and the type of DLC played a crucial role in the development and composition of the tribolayer and the friction performance. The additive package contained in the fully formulated (FF) oils limited the friction reduction capabilities of MoDTC additive for every material pair. Accelerated a-C:H coating wear related to MoDTC tribochemistry was found. For the first time, it has been shown that a distinctive MoS2-containing tribolayer can be formed on the ta-C surface, leading to a coefficient of friction lower than 0.04. The underlying mechanisms of MoDTC/surface interactions and their effect on friction and wear are discussed.

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The use of additive manufacturing (AM) is widely advancing the scope of rapid prototyping and manufacturing in tribological applications and material science research. However, there is still limited research focused on investigating the frictional and wear performance of AM polymers, especially of Polyjet manufactured parts. This work focuses on the effect of varying the contact load on the friction and wear mechanisms of additively manufactured acrylonitrile butadiene styrene (3D ABS) and Verogray polymers fabricated using Polyjet technology. Loads of 1, 5 and 10 N were applied under dry sliding contact with a 52100 steel counterface at room temperature. Dependence of friction and wear on the surface orientation to the sliding direction is noted. The results demonstrate that at 1 N load, the friction coefficient is primarily dependent on the orientation of the surface to the sliding direction. However, at higher loads of 5 N and 10 N, this dependency is shown to be a function of the bulk material properties rather than the surface roughness. Further correlation between the surface morphology and wear rate is shown to be dependent on the bulk material properties and the applied load. The results from this study provide alternate application uses for Polyjet materials in metal-polymer tribo-contacts for improved friction and wear performance.