Krytox

About: Krytox is a research topic. Over the lifetime, 98 publications have been published within this topic receiving 2012 citations.

Fluorous membrane-based separations and reactions

Abstract: Porous alumina membranes were rendered compatible with fluorous liquids by surface modification with a carboxylic acid terminated perfluoropolyether (Krytox 157FSH). FTIR and contact angle measurements demonstrate the success of the modification.Fluorous liquids are readily imbibed by modified alumina membranes, resulting in fluorous supported liquid membranes. Fluorine-containing organic solutes are selectively transported through the fluorous supported liquid membranes. Selectivity is defined as the permeability of a fluorous tagged solute over an analogous organic compound. The membrane modification conditions (reagents, concentrations, reaction time) were optimized to maximize the selectivity. The membrane pore size affects the solute permeabilities and selectivities.Two series of homologous esters of perfluoroalkanoic acids with different organic moieties were studied. Permeability increased for both series as the perfluoroalkyl chain was lengthened. This shows that the difference in permeabilities is dominated by partitioning rather than diffusion. We further measured the partition coefficients of the homologs. The free energy of transfer of a ¨CCF2¨C group (ethanol to perfluorinated solvents) is -1.1 kJ/mol. The experimental values of the partition coefficients are well correlated with the i®mobile order and disorderi¯ theory. This provides an easy way to estimate partition coefficients in any biphasic system, even for solvents that are fluorous mixtures. Diffusion coefficients were determined from permeabilities and partition coefficients based on the solution-diffusion model of permeability. Measured values are satisfactorily related to the Stokes-Einstein equation, especially for higher homologs. This investigation enables the prediction of transport properties of the fluorous supported alumina membranes.Krytox 157FSH, which is virtually insoluble in any but fluorous solvents, was deposited on the fluorous-modified alumina membranes. FTIR shows the presence of the H-bond-based carboxylic acid dimers for these adsorbed Krytox 157FSH molecules. The carboxylate groups of Krytox 157FSH extract cations from aqueous solutions.

The Effects of Acid Passivation, Tricresyl Phosphate Presoak, and UV/Ozone Treatment on the Tribology of Perfluoropolyether-Lubricated 440C Stainless Steel Couples

Abstract: The boundary-lubrication performance of two perfluoropolyether (PFPE) thin films in the presence of passivated 440C stainless steel is presented. The study used a standard ball on disk (BoD) tribometer in dry nitrogen and a vacuum spiral orbit tribometer (SOT). Stainless steel surfaces were passivated with one of four techniques: high and low temperature chromic acid bath, a tricresyl phosphate (TCP) soak, or UV/Ozone treated for 15 min. After passivation, each BoD disk had a 400A film of Krytox 16256 (PFPE) applied to it. The lifetimes of these films were quantified by measuring the number of sliding cycles before an increase in friction occurred. The lubricated lifetime of the 440C couple was not altered as a result of the various passivation techniques. The resulting surface chemistry of each passivation technique was examined using X-ray photoelectron spectroscopy (XPS). The SOT was used to examine the effects of the TCP treatment on the lubricated lifetime of another PFPE, Brayco 815Z, under rolling conditions. None of the passivation techniques were found to dramatically increase the oxide film thickness or lubricated lifetimes.

Tribological Behavior of Nano-Onions in Krytox 143AB Evaluated

Abstract: Nanoparticles have been developed over the past 10 years and have found several applications. This work presents the use of carbon nano-onions as a potential oil additive for aerospace applications. Researchers at the NASA Glenn Research Center tested lubricant lifetimes in ambient air and ultrahigh vacuum and characterized the breakdown products of the friction and wear. These carbon nanoparticles can provide adequate lubrication very similar to that of graphitic material when run in air. Soot represents one of the very first nanostructured materials, although it has rarely been considered as such. Changes in the carbon nanostructure, resulting in increased graphitic layer plane length, correlate with reactivity loss. Upon heating spherically shaped nanometer-sized carbon black in the absence of oxidant, graphene sheets form, and the initial soot particle templates the growth of a graphitic particle into what is best described as a sphere with many flat sides having a hollow interior. Because there are no edge sites, these polygonal graphitic particles, or nano-onions, are relatively resistant to oxidation. Graphite is used as a solid lubricant because of its stability at moderately high temperatures. However, the temperature at which graphite oxidizes rapidly is strongly influenced by surface area. With the size of particles typically employed in lubrication, a great amount of thermal stability is lost because of size reduction either during preparation or during lubrication of contacting parts. Therefore, we have undertaken a study of the lubricating ability of graphitic nano-onions (ref. 1).