Adsorption of alcohols and fatty acids onto hydrogenated (a-C:H) DLC coatings

Abstract

Information about the interactions between lubricants and DLC coatings is scarce, despite there having been many studies over the years. In this investigation we used ToF-SIMS, XPS and contact-angle analyses to examine the adsorption ability and mechanisms with respect to two oiliness additives, i.e., hexadecanol and hexadecanoic acid, on an a-C:H coating. In addition, we analyzed the resistance of the adsorbed films to external influences like solvent cleaning. The results show that both molecules adsorb onto surface oxides and hydroxides present on the initial DLC surface and shield these structures with their hydrocarbon tails. This makes the surfaces less polar, which is manifested in a smaller polar component of the surface energy. We also showed that ultrasonic cleaning in heptane has no significant effect on the quantity of adsorbed molecules or on their chemical state. This not only shows the relatively strong adsorption of these molecules, but provides useful information for future experimental work. Of the two examined molecules, the acid showed a greater adsorption ability than the alcohol, which explains some of the previously reported better tribological properties in the case of the acid with respect to the alcohol. This peer reviewed manuscript has been accepted for publications to the Lubrication Science.

Ultra-Low Friction on Tetrahedral Amorphous Diamond-Like Carbon (ta-C) Lubricated with Ethylene Glycol

“…For example, the creation of graphite-like patches on the coatings could be established for taC/taC tribocontacts by means of XPS [10]. SIMS allowed for the detection of lubricant-fragments [11][12][13][14][15][16][17][18], although the detected fragments have not yet been correlated with the different friction levels. Very low friction regimes can be associated with the formation of a transfer layer.…”

Improving frictional properties of DLC films by surface energy manipulation

“…Thus it can be seen that, via a simple two-step process, the controllable modify of DLC can be achieved successfully. In addition, by using the contact angle measure of two solutions with big polarity different and the OWRK (OwensWendt-Rabel-Kaelble) method (eqn (2)), 8,27 the surface energies and their components of as-modied simples can be calculated easily. In order to ensure the accuracy of results, the deionized water with strong polarity and CH 2 I 2 reagent with low polarity are selected.…”

Green Tribology for the Sustainable Engineering of the Future

“…For example, original, innovative approaches include chemical-based interactions with organic, environmentally adapted chemistry [20] and [21], and especially biodegradable lubricants (Fig. 3).…”