Perfluoropolyalkyl Ether Research Articles

Grease-lubricated tribological behaviour of nitrided layer on 2Cr13 steel in vacuum

Tribological behaviour of the nitrided layer sliding against self-mating under dry sliding and grease-lubricated conditions in vacuum was investigated on a pin-on-disk type tribometer, with the interaction among the nitrided layer and grease being focused on. The morphologies of the worn surfaces were observed by scanning electron microscopy (SEM). The chemical states of typical elements on the worn surfaces of the nitrided disks and pins were examined by means of X-ray photoelectron spectroscopy (XPS). The chemical compositions of grease samples taken from worn surfaces on the nitrided disks were analysed by Fourier transform infrared spectroscopy (FTIR). Experimental results show that under grease-lubricated conditions, the nitrided layer exhibits lower average friction coefficient and higher wear resistance than those for the dry sliding. In the former case, the wear of nitrided layer shows a transition from the mild adhesive to the severe adhesive wear and even to the delamination wear, with increasing normal load from 10 to 90 N. In the latter case, a transition takes place from the mild abrasive wear to the micro-fatigue type one with increasing the normal load. Tribochemical reactions occur between the nitrided layer and perfluoropolyalkyl ether (PFPE) grease during the lubricated sliding of the nitrided disks against self-mating in vacuum.

Interaction of Alcohols and Ethers with a-CFx Films

The surfaces of the magnetic data storage hard disks used in computers are coated with a thin film of amorphous carbon and a layer of perfluoropolyalkyl ether (PFPE) lubricant. Both protect the surface of the magnetic layer from contact with the read-write head flying over the disk surface. Although the most commonly used carbon films are amorphous hydrogenated carbon, a-CH(x), it has been suggested that the thermal properties of amorphous fluorinated carbon films, a-CF(x), might be superior. This work has probed the interaction of small fluorinated ethers and alcohols with the surfaces of a-CF(x) films to understand the effects of carbon film fluorination on the interaction of the lubricant with its surface. Temperature-programmed desorption was used to measure the desorption energies of small fluorocarbons from the a-CF(x) surface and to compare their desorption energies with those from the surfaces of a-CH(x) films. These measurements reveal that, similarly to a-CH(x) films, a-CF(x) films expose a heterogeneous surface on which fluorocarbons adsorb at sites with a range of binding energies. The fluorocarbon ethers all have lower heats of adsorption than their hydrocarbon counterparts, suggesting that the ethers adsorb by donation of electron density from the oxygen lone-pair electrons to sites on the surface. Fluorinated alcohols have roughly the same heats of adsorption as their hydrocarbon counterparts. There is little significant difference between the interactions of fluorinated ethers (or alcohols) with the surfaces of either a-CF(x) or a-CH(x) films.

Effects of Perfluoropolyalkyl Ethers and Perfluorinated Acids on Crack Growth in Soda-Lime Glass

The growth of cone cracks in soda-lime glass during static loading with a spherical indenter shows that crack growth is accelerated by perfluorinated acids, probably by a stress corrosion mechanism involving reaction between the acids and strained Si-O bonds in the crack-tip region. The strained bonds are not reactive toward perfluoropolyalkyl ether (PFPE) oils under static conditions. In hybrid silicon nitride-steel contacts, acidic products of the degradation of PFPE oils by Lewis acid sites on the steel surfaces may be transported through the crack to the crack-wake region and attack the strained Si-O bonds. These results suggest that PFPE oils may not be the best choice for lubrication of silicon nitride-steel hybrid bearing systems.

Desorption Kinetics and Energetics of Monodisperse Fomblin Zdol from Carbon Surfaces

Desorption is one of the mechanisms of lubricant loss from the surfaces of data storage media. This work has studied the desorption of monodisperse samples of a typical perfluoropolyalkyl ether lubricant, Fomblin Zdol, from the surface of graphite. Desorption is observed to occur molecularly through a first-order process with an energy barrier to desorption, Δ , that is independent of coverage but is dependent on molecular weight. The Δ of 994 and 1329 g/mole fractions were found to be 128 ± 2 kJ/mol and 155 ± 2 kJ/mol, respectively. The pre-exponents, v, of the first-order desorption rate constant were found to have values of 1019.6±0.3 s-1 and 1021.1±0.3 s-1 for the 994 and 1329 g/mole Zdol fractions, respectively. These results clearly reveal the chain length dependence of the Δ , and the high values of the pre-exponents are similar to those observed for desorption of other oligomeric species from graphite.

Alkane Contamination Effects on PFPE Lubricant Bonding to a-CHx Overcoats

Increasing operating temperatures within hard disk drives promote increased outgassing from drive components and thus can adversely influence the durability and reliability of hard disk drives. This study investigates the effects of hydrocarbon contamination on the bonding of perfluoropolyalkyl ether (PFPE) lubricants to amorphous hydrogenated carbon (a-CHx) overcoats. This work has used decane (C10H22 )a s a model for the hydrocarbon contamination present in drives and perfluorodiethyl ether ((CF3CF2)2O) and 2,2,2-trifluoroethanol (CF3CH2OH) as models for the backbone and endgroups, respectively, of the common disk lubricant Fomblin Zdol. Temperature-programmed desorption experiments were conducted using CF3CH2OH coadsorbed with C10H22 on an a-CHx overcoat and (CF3CF2)2O coadsorbed with C10H22 on an a-CHx overcoat. The results indicate that the presence of C10H22 decreases the adsorption energies of both CF3CH2OH and (CF3CF2)2O on the a-CHx overcoats. The implication of these results is that the mobility of PFPE lubricant films can be increased by the presence of hydrocarbon contaminants on the disk surface.

Adsorption of Fluorinated Ethers and Alcohols on Graphite

As part of a research program to determine the nature of the interactions of perfluoropolyalkyl ether lubricants with the surfaces of magnetic data storage media, we have studied the desorption of several model compounds from the surface of graphite. In this instance we have been modeling the chemical functionality of the lubricant Fomblin Zdol by using perfluorodiethyl ether ((CF3CF2)2O) to represent the ether linkages of its backbone and 2,2,2-trifluoroethanol (CF3CH2OH) to represent its hydroxyl end groups. The desorption kinetics of these compounds from the basal plane of graphite have been compared with those of their hydrocarbon analogues (CH3CH2)2O and CH3CH2OH. More importantly, the desorption of these compounds from graphite has been compared with prior measurements of their desorption from numerous types of amorphous carbon films. The desorption from graphite occurs with zero-order kinetics and well-defined desorption energies. The results of these measurements indicate that the broad distributi...

Humidity Effects on PFPE Lubricant Bonding to a-CHx Overcoats

The continued reduction in the head−disk separation of magnetic data storage systems and the corresponding increase in the frequency of head−disk contacts will place severe stress on the lubricant and overcoat used to protect the surfaces of magnetic media. With decreasing fly heights, environmental conditions such as temperature and humidity that influence the lubricant−overcoat interactions become increasingly important to the tribological performance of the head−disk interface. It is essential to obtain a fundamental understanding of the molecular interactions at the lubricant−overcoat interface in order to maintain the reliability of future hard disk drives. The coadsorption of model fluoro alcohols and fluoro ethers with water was studied to gain a fundamental understanding of the effects of humidity on the bonding of perfluoropolyalkyl ether (PFPE) lubricants to amorphous hydrogenated carbon (a-CHx) overcoats. Temperature-programmed desorption experiments were performed using 2,2,2-trifluoroethanol (CF3CH2OH) coadsorbed with water and perfluorodiethyl ether [(CF3CF2)2O] coadsorbed with water. The results indicate that the presence of water increases the desorption energy of CF3CH2OH on the a-CHx overcoat but decreases the desorption energy of (CF3CF2)2O on a-CHx overcoats. The implication of these results is that there is a net increase in the mobility of PFPE lubricant films when exposed to humid environments.

Bonding of Ethers and Alcohols to a-CNx Films

The surface chemistry of fluorinated ethers and fluorinated alcohols adsorbed on amorphous nitrogenated carbon (a-CNx) have been studied as models for the interaction of perfluoropolyalkyl ether (PFPE) lubricants with the surfaces of magnetic data storage media. Temperature-programmed desorption experiments conducted in ultrahigh vacuum using small fluorinated ethers and fluorinated alcohols have measured their desorption energies and have provided insight into the nature of bonding between PFPEs and a-CNx films. Preliminary results indicate that ether linkages interact with a-CNx films through electron donation from the oxygen lone pair electrons. In contrast, alcohol end groups show evidence of hydrogen bonding with a-CNx films. The models derived from this study can aid in the future development of both lubricants and protective overcoats to ensure that the magnetic hard disks display optimal wear resistance and performance.

In situ study of multialkylated cyclopentane and perfluoropolyalkyl ether chemistry in concentrated contacts using ultraviolet Raman spectroscopy

In situ analysis of lubricated, concentrated contacts can be performed using ultraviolet Raman spectroscopy. An ultraviolet Raman spectrometer has been constructed and interfaced to a ball-on-flat tribology apparatus. Two lubricants have been studied under various loads with and without pure sliding: (1) a mixture of perfluoropolyalkyl ethers (Krytox 143AC), and (2) a mixture of high molecular weight multialkylated cyclopentanes (2001A). Results show that without sliding, Krytox and 2001A remain stable under the various loads used. When sliding was applied, both Krytox and2001A undergo chemical decomposition to amorphous carbon (friction polymer). An analysis of the Raman spectra shows a structural difference between the amorphous carbon produced from Krytox and that produced from 2001A. Results also demonstrate the importance of in situ analysis since the composition at the contact center during and after sliding are different.

The decomposition reaction path of a linear PFPAE under tribological conditions

It has previously been shown using 19F nuclear magnetic resonance (NMR) spectroscopy that a linear perfluoropolyalkyl ether (PFPAE) fluid undergoes decomposition by a disproportionation reaction mechanism to form acid fluorides when heated in the presence of aluminum chloride. It is shown in this study that the same linear PFPAE fluid decomposes by the same reaction mechanism to form the same acid fluorides when heated at 345°C in the presence of dry air and bearing steels. Then, it is shown that these acid fluorides readily undergo hydrolysis to carboxylic acids when they are exposed to atmospheric moisture. Finally, carboxylic acids were detected in highly stressed linear PFPAE fluids exposed to the atmosphere after recovery from fatigue testing experiments. Therefore, it is concluded that under real tribological conditions, linear PFPAE fluids initially decompose in the presence of bearing steels by a disproportionation reaction mechanism to form acid fluorides which subsequently react with atmospheric moisture to form carboxylic acids.

Effect of Fluorine on the Bonding and Orientation of Perfluoroalkyl Ethers on the Cu(111) Surface

By using small fluorinated ethers as models for perfluoropolyalkyl ether lubricants, we have been able to determine the effect of fluorine on the bonding and orientation of the alkylethers adsorbed on the Cu(111) surface. The desorption energies have been determined by using temperature-programmed desorption and the orientations by Fourier transform infrared absorption reflection spectroscopy (FT-IRAS). The model compounds studied were dioxolane (CH2OCH2OCH2) and perfluorodioxolane (CF2OCF2OCF2), diethyl ether ((CH3CH2)2O) and perfluorodiethyl ether ((CF3CF2)2O), dimethoxymethane ((CH3O)2CH2) and perfluorodimethoxymethane ((CF3O)2CF2), dimethyl ether ((CH3)2O) and perfluorodimethyl ether ((CF3)2O). All of the molecules studied adsorb molecularly and reversibly on the Cu(111) surface exhibiting first-order desorption kinetics. Upon fluorination of the alkyl ethers, the adsorbate−metal bond was weakened by 5−7 kcal/mol. The hydrogenated ethers exhibit repulsive adsorbate−adsorbate interactions, while the fluorinated ethers have attractive adsorbate−adsorbate interactions. At saturation coverages, the FT-IRAS spectra show that the diethyl ethers are oriented with their molecular axes parallel to the Cu(111) surface. 1,3-Dioxolane was oriented with its ring plane parallel to the metal surface.

Acidic Attack of Perfluorinated Alkyl Ether Lubricant Molecules by Metal Oxide Surfaces

The reactions of linear perfluoropolyalkylether (PFAE) lubricants with α-Fe2O3 and Fe2O3-based solid superacids were studied. The reaction with α-Fe2O3 proceeded in two stages. The first stage was an initial slow catalytic decomposition of the fluid. This reaction released reactive gaseous products which attacked the metal oxide and converted it to FeF3. The second stage was a more rapid decomposition of the fluid, effected by the surface FeF3. A study of the initial breakdown step was performed using α-Fe2O3, α-Fe2O3 preconverted to FeF3, and sulfate-promoted α-Fe2O3 superacids. The results indicate that the breakdown reaction involves acidic attack at fluorine atoms on acetal carbons in the linear PFAE. Possible approaches to combat the problems are outlined.