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Li, P.; Lyth, E.; Munro, D.; Ng, Lily

doi:10.1023/a:1019155221917

Cited by 9 publications

(8 citation statements)

References 32 publications

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“…Skeletal Degradation of CF 3 OCF 2 CH 2 OH. Polyperfluoroethers are known to undergo catalytic degradation, to form products such as COF 2 , − when in contact with Lewis acids . A degradation reaction path that leads to the formation of COF 2 is the unimolecular decomposition reaction originating from a transition state The geometry of the transition structure (ZDTS) is presented in Figure , and the optimized structural parameters for ZDTS are summarized in Table .…”

Section: Resultsmentioning

confidence: 99%

Computer-Modeling Study of the Interactions of Zdol with Amorphous Carbon Surfaces

1999

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The formation of a tribologically reliable interface between the magnetic recording disk and the magnetic recording head in hard-disk drives is predicated upon the presence of a molecularly thin perfluoropolyether (PFPE) lubricant film. The molecular interactions that develop between the PFPE lubricant and the underlying amorphous carbon overcoat of the magnetic recording disk govern the adhesion, physical coverage, thermal stability, and mobility of the lubricant on the carbon surface and hence are of paramount importance in defining the tribological performance of the drive. In this work, information pertaining to the interfacial interactions between the hydroxyl-terminated PFPE lubricant Zdol and amorphous carbon surfaces is obtained via ab initio calculations. The small fluorinated ether molecules CF3OCF2CH2OH (ZD) and CF3OCF3 (PFDME) were used as computationally tractable models for the PFPE lubricants. A population analysis is performed on the ZD model lubricant and the various chemical functionalities known to exist on amorphous carbon surfaces. In the case of an amorphous, hydrogenated carbon surface, CHx, the adhesive interactions of the PFPE backbone with the nonpolar component of the carbon surface were modeled by the interaction of ZD with simple hydrocarbons. The attractive van der Waals interactions that result are comparatively weak and insufficient at room temperature to overcome the associated decrease in entropy. As a consequence, these interactions will not contribute significantly to the adhesion of PFPE's to the carbon surfaces under disk-drive operating conditions. The primary source of adhesion in the Zdol−CHx system stems from hydrogen bonding of the hydroxyl end groups of the Zdol lubricant with the carboxylic acid and ketone functionalities on the CHx surface. The computed binding energies of the ZD + ketone and ZD + carboxylic acid interactions are −11 and −15 kcal/mol, respectively. These interaction strengths are large enough to compensate for the entropy decrease and hence result in a net decrease in the free energy. In addition to these thermodynamically stable adhesive interactions, the computed binding energy of the cohesive hydrogen-bonding interactions between ZD molecules is significant. The formation of a highly associated, two-dimensional structure is therefore possible for molecularly thin Zdol films on carbon surfaces. Amorphous nitrogenated carbon, CNx, can also provide strong physisorption sites for Zdol. The interaction of ZD with imine and nitrile functionalities were studied. The interactions of the hydroxyl end group with imine centers is strongly attractive, leading to the formation of a hydrogen bond with a strength of −16 kcal/mol. Interactions with nitrile sites are somewhat less favorable with a computed binding energy of −10 kcal/mol. The nitrogen centers on CNx are negatively charged, and hence repulsive interactions with the negatively charged perfluoroalkyl ether backbone are expected. The modeling results are then used to interpret previous experimental resu...

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Section: Resultsmentioning

confidence: 99%

Computer-Modeling Study of the Interactions of Zdol with Amorphous Carbon Surfaces

1999

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“…Previous studies of our group [9][10][11][12][13] as well as Basu et al [14] and Chen et al [15], on the interaction of partially and fully fluorinated ethers with high-surface-area alumina oxide have shown that surface hydroxyl groups and Lewis acid sites play a significant role in the process of catalyzing thermal decomposition of these compounds on alumina surfaces.…”

Section: Introductionmentioning

confidence: 74%

Surface chemistry of fluoroethanols

Vaynberg

2005

Surface Science

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“…Studies have shown that upon heating, the degradation of PFPEs is catalyzed by the Lewis acid Al 2 O 3 (alumina). ,,− Alumina and other metal oxides are present in computer disks and the reading heads of magnetic hard disk drive systems, and the metal oxides come into contact with the PFPE lubricant and therefore have the potential to degrade the lubricant. − , The surface sites present on alumina are similar to certain species found on clay mineral surfaces; therefore, soil particles could catalyze the degradation of PFPEs through mechanisms similar to those proposed for degradation on aluminum oxides. In fact, high-molecular-weight organic compounds have been shown previously to adsorb strongly to alumina and aluminosilicates found in natural waters .…”

Section: Introductionmentioning

confidence: 99%

“…The catalytic centers on alumina are suggested to be defect Al 3+ surface sites and hydroxyls. ,,, Using Fourier transform infrared spectroscopy (FTIR), Li et al examined the interactions of CF 3 CF 2 OCF 2 CF 3 and CF 3 OCF 3 with Al 2 O 3 under vacuum and proposed that hydroxyl sites on the Al 2 O 3 surface play an important role in the decomposition of these simpler PFPEs …”

Section: Introductionmentioning

confidence: 99%

“…The catalytic centers on alumina are suggested to be defect Al 3+ surface sites and hydroxyls. 9,11,13,18 Using Fourier transform infrared spectroscopy (FTIR), Li et al examined the interactions of CF 3 CF 2 OCF 2 CF 3 and CF 3 OCF 3 with Al 2 O 3 under vacuum and proposed that hydroxyl sites on the Al 2 O 3 surface play an important role in the decomposition of these simpler PFPEs. 11 Upon the basis of a study using an ultrahigh vacuum drag test, Zhang et al suggested that a coordination bond forms between the Al atom of Al 2 O 3 and the O atom of the PFPE, leading to the degradation of the PFPE.…”

Section: Introductionmentioning

confidence: 99%

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NMR Studies of the Thermal Degradation of a Perfluoropolyether on the Surfaces of γ-Alumina and Kaolinite

et al. 2007

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Solid-state nuclear magnetic resonance (NMR) methods are used to follow the thermal degradation of Krytox 1506, a common perfluoropolyether, following adsorption onto the surfaces of gamma-Al2O3 and a model clay (kaolinite). The alumina studies are complemented with thermogravimetric analysis (TGA) to follow the degradation process macroscopically. Molecular-level details are revealed through 19F magic-angle spinning (MAS), 27Al MAS, and 19F --> 27Al cross-polarization MAS (CPMAS) NMR. The CPMAS results show the time-dependent formation of probable VIAl(O6 - nFn) (n = 1, 2, 3) species in which the fluorine atoms are selectively associated with octahedrally coordinated aluminum atoms. For the alumina system, the changes in peak shapes of the CP spectra over time suggest the early formation of catalytically active degradation products, which in turn lead to the formation of additional perfluoropolyether degradation products. Similar to the alumina system, the kaolinite system also displays new resonances in both the 27Al MAS and 19F --> 27Al CPMAS spectra after thermal treatment at 300 degrees C for up to 20 h but reveals a more distinct species at -15.5 ppm that forms at the expense of an initial species (3 ppm), which is in greater abundance at shorter heating times.

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Untitled

Cited by 9 publications

References 32 publications

Computer-Modeling Study of the Interactions of Zdol with Amorphous Carbon Surfaces

Computer-Modeling Study of the Interactions of Zdol with Amorphous Carbon Surfaces

Surface chemistry of fluoroethanols

NMR Studies of the Thermal Degradation of a Perfluoropolyether on the Surfaces of γ-Alumina and Kaolinite

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