Photophysical comparative study of amylose and polyvinyle pyrrolidone / single walled carbon nanotubes complex

Progressive addition of hydroxypropylated amylose (AmH), from 0.05 wt% to 4.5 wt%, to single-walled carbon nanotubes (SWNTs) in aqueous surfactant suspensions quenches the intrinsic near-Infra-Red fluorescence of semiconducting SWNTs while dispersions obtained with a same amount of polyvinylpyrrolidone (PVP) remain luminescent. Near Infra-Red emission spectroscopy (fluorescence and Raman scattering) of the samples is used to characterize the supramolecular organization of these polymer/SWNT complex. The SWNTs are found to be wrapped by the PVP chains and not by the AmH chains which rather form AmH/surfactant/SWNTs complex. In PVP/SWNTs dispersion, the fluorescence line position and intensity are affected by dielectric screening. In the case of AmH/surfactant/SWNTs complex, dielectric screening plays also a role but quenching occurs above about 3 wt % of AmH. We attribute the quenching to the formation of a “composite like” microstructure by opposition to stabilized dispersion

Macro- and Nanotribological Properties of Graphite Tribofilms: Influence of the Sliding Interface

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BIOMASS CARBONS AS ADDITIVES FOR LUBRICATION: FRICTION REDUCTION KEY PARAMETERS

International audienceIn boundary lubrication regime, friction reduction and antiwear processes are associated to the presence of additives in the lubricating oils or greases. These processes are due to the formation of protective tribofilms resulting from chemical reactions between the additives and the sliding surfaces, in the physico-chemical conditions of the sliding contact. But the main problems encountered with conventional additives (transition metal dithiophosphates or carbamates) are their inefficiency in the case of non metallic surfaces and the film formation period (induction period), in which the contacting surfaces undergo sever wear. Recently developed lubrication strategies consist in the use of dispersion in oils of nano additives able to build the protective tribofilm in the sliding contact without reaction with the surfaces [1]. We pointed out in previous studies the good friction reduction properties of various (nano) carbon materials [2, 3]. This work is concerned with the use of activated carbons synthetized from biomass as new additives for lubricants. Special attention is paid to the role of the carbon structure, in terms of morphology, size, (nano)structuration, porosity of the carbon particles on the friction properties of the additives. 1 Mansot, J.L, et al, Brazil

Tribological properties of Sargassum carbon dots as additives in water-based lubricants

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CONTRIBUTION TO THE FORMULATION OF GREEN LUBRICANTS USING LOCAL BIOMASS

International audienceFriction and wear are the first causes of the decrease of the performances and the durability in mechanical systems. The role of lubrication is to minimize friction between the sliding surfaces to protect them from wear. Conventional liquid lubricants are constituted of a base oil and solid additives particles presenting specific properties, such as friction reduction and antiwear performances. The role of friction reducers is to ensure the lubricating performances in boundary lubrication regime. Commercial lubricants generally use graphite and petroleum-based oils because of their recognized lubricating properties, their stability and low cost. However, such lubricants induce health and environmental hazards due to their life cycle. The aim of this work is to investigate the possibility to use local biomass in order to produce environmentally-friendly lubricants. Local vegetable oils are interesting candidates because of their inherent qualities like renewability, bio-degradability, non-toxicity. This work shows that such natural oils present better friction performances than petroleum-based ones. Then considering friction reduction additives, the tribological behaviour of activated carbons synthetized from biomass is evaluated and special attention is paid to the role of the carbon structure, in terms of morphology, size, porosity of the carbon particles on the friction properties of the additives. The tested activated carbons are obtained from either terrestrial (sugar cane bagasse, banana tree, etc.) or alga (sargassum alga) precursors. Very good friction performances are observed by selecting the adequate precursor and tunning the activation experimental conditions. Finally, the determination of the tribological properties of activated carbons/natural oils mixtures results in the first formulation step of our lubricant made from local biomass

Utilisation des carbones issus de la biomasse en lubrification

International audienceLes phénomènes de frottement et d’usure sont les causes principales des pertes de performances et de durabilité des systèmes mécaniques. Les techniques de fabrication de pièces métalliques telles que les engrenages, les roulements à billes, les segments, pistons et chemises, doivent répondre aux exigences économiques grandissantes du marché, comme l’amélioration de la durabilité des matériaux, l’augmentation des performances, la réduction du coût de la maintenance, ou encore la baisse de la consommation en énergie. Le recours à la tribologie, définie comme la science qui étudie les phénomènes de frottement, d’usure et de lubrification, est alors primordial et constitue un enjeu économique important. Les résultats d’une étude publiée par le Cetim en 1994 confirment que l’économie potentiellement réalisable serait de l’ordre de 26 milliards d’euros par an en France, soit 1% du PIB (chiffres de 2010), si toutes les connaissances acquises en tribologie étaient appliquées à l’industrie [1].C'est la lubrification qui a pour rôle de minimiser le frottement et de protéger les surfaces de l'usure. La stratégie mise en place pour lutter contre ces phénomènes consiste à introduire un lubrifiant entre les surfaces frottantes. Ce lubrifiant peut être solide, liquide ou gazeux, et il doit permettre d’empêcher le contact direct entre les surfaces. Plusieurs régimes de lubrification sont identifiés : hydrodynamique, élastohydrodynamique, mixte et limite. Ils dépendent des vitesses de déplacement relatif des surfaces, de la viscosité du lubrifiant et de la charge supportée par le contact, et sont caractérisés par des épaisseurs de films lubrifiants variées, divers coefficients de frottement et des usures associées différentes. Le régime de lubrification limite sera étudié car il conduit aux coefficients de frottement les plus élevés et aux plus fortes usures. Ce régime limite est rencontré pour une faible vitesse de glissement et une charge élevée.Les bases lubrifiantes pures (huile minérale ou de synthèse) ne pouvant assurer toutes les fonctions protectrices, des additifs sont ajoutés afin d’améliorer leurs propriétés réductrices de frottement et d’usure. Les nouvelles stratégies de lubrification utilisent des particules colloïdales en dispersion dans les lubrifiants. L’approche consiste à approvisionner le contact glissant en particules solides, susceptibles de constituer instantanément le film tribologique. Les matériaux lamellaires, tel le graphite, sont généralement de bons candidats, leur structure en feuillets assurant de bonnes propriétés tribologiques.Ce travail porte sur la revalorisation de la biomasse locale dans le domaine de la lubrification. L’utilisation de charbons actifs en tant qu’additifs solides dans un mélange huile végétale/huile de base est étudiée. L’influence des paramètres entrant dans la phase de synthèse des charbons actifs est également étudiée, tels que température et durée de pyrolyse, type de précurseurs, mode d’activation. Des mélanges huiles végétale/huile de base/additifs carbonés sont effectués dans diverses proportions afin d’optimiser les propriétés tribologiques en vue de la formulation d’un nouveau lubrifiant, plus respectueux de l’environnement qu’un lubrifiant minéral actuel

Tribological properties of fluorinated nanocarbons with different shape factors

International audienceThe structural parameters of fluorinated nanocarbons presenting different shapes, i.e. spherical, tubular and discotic are investigated and correlated to their tribological properties. Different fluorination rates of graphitized carbon blacks (0D), carbon nanofibres (1D) and a mixture of carbon nanodiscs and nanocones (2D) were achieved under pure molecular fluorine gas flow (direct fluorination). Raman spectrometry, X-ray diffraction and 19F solid state nuclear magnetic resonance underline similar structure and nature of the C-F bonds (covalent) for equivalent fluorine contents. In spite of the similarities of physical-chemical properties at equivalent fluorine contents, the tribological properties of the fluorinated nanocarbons differ. Those properties are discussed taking into account the role of the fluorine content and location of the fluorine atoms in the decrease of the interparticle interactions and in the cleavage of the external fluorocarbon layers to form the tribofilm. Finally, the effect of the shape is discussed

Mechanisms of MoS2 formation by MoDTC in presence of ZnDTP: effect of oxidative degradation

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