Bonding to the underlying carbon surface of some novel one-component PFPE boundary lubricants based on anisole and hydroxyl mixture end groups

2019 ◽  
Vol 20 ◽  
pp. 100206
Author(s):  
R.J. Waltman ◽  
A. Fan
Keyword(s):  
Carbon Surface ◽  
End Groups ◽  
Boundary Lubricants

Molecular Orientation of Polymer Lubricant Films: Its Tribological Consequence

1998 ◽  
Vol 120 (2) ◽  
pp. 369-378 ◽  
Author(s):  
Chao Gao ◽  
Tam Vo ◽  
Joel Weiss
Keyword(s):  
Molecular Orientation ◽  
Energy State ◽  
Tribological Performance ◽  
Lubricant Film ◽  
Carbon Surface ◽  
Lubricant Layer ◽  
Significant Difference ◽  
End Groups ◽  
Lubricant Films ◽  
Almost All

The objective of this paper is to demonstrate, from experiments and modeling, how and why molecular orientation of functional end groups of perfluoro-polyether (PFPE) lubricants play an important role in the tribological performance of thin film magnetic disks. These disks typically have an amorphous carbon overcoat upon which a thin lubricant layer is deposited using dip-coating technique. Glancing-angle FTIR (Fourier Transform Infra-Red Spectrometry) is used for measuring molecular orientation of planer functional end groups. A molecular orientation index (MOI) was defined as 1 for randomly oriented functional end groups. The MOI is mathematically derived as 3 (maximum) for lubricant molecules oriented with their functional end groups perpendicular to the surface, and as 0 (minimum) if lubricant molecules oriented with their functional end groups parallel to the surface. The MOI is shown to depend on processing conditions and lubricant film thickness. The tribological performance of the lubricant films was evaluated using drag-mode contact start-stop testing. It was found that wear durability of the lubricant films (~2 nm) with MOI ~ 1.5 is a few times better than those with MOI ~ 0.5 to 1.0. No significant difference in the amount of bonded lubricant film was detected over the range of MOI studied. Nor was there a detectable relationship with hydrophobicity. It was inferred from decreased MOI values due to thermal effects and storage time that a smaller MOI value corresponds to a lower free energy state of the lubricant film. Interestingly, MOI values for bonded lubricant films for Process A are found to be close to 3.0, suggesting that almost all functional end groups in the bonded films are oriented perpendicular to the carbon surface, close to 2.0 for process B, and close to 0 for process C, meaning that almost all functional end groups in the bonded films from process C are oriented parallel to the carbon surface. Relationship between physical/chemical bonding configurations and MOI values are graphically presented in detail. Based on this relation, a simple model on lubricant film structures for the three processes studied is presented. The model MOI values agree very well with measured MOI values as a function of lubricant thickness for all three processes, and the model also appears to account for the observed tribology performance for the MOI values studied (0.5 ~ 1.5).

Novel One-Component Anisole- and Hydroxyl-Terminated Perfluoropolyethers for Boundary Lubrication

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Ao Fan ◽  
Connie Wiita ◽  
Robert J. Waltman
Keyword(s):  
Film Thickness ◽  
Single Component ◽  
Hydroxyl Groups ◽  
Film Properties ◽  
Lubricant Transfer ◽  
Boundary Lubricant ◽  
Boundary Film ◽  
End Groups ◽  
Boundary Lubricants ◽  
Physical Mixtures

The tribological properties of some novel single component perfluoropolyether (PFPE) boundary lubricants with chemically integrated mixture end groups are investigated. Chemically integrated mixture end groups composed of hydroxyl- and anisole-terminated PFPE boundary lubricant films on the –(CF2CF2CF2O)– main chain are reported. These PFPE-based boundary lubricants explore a new method by which single component PFPE lubricants with mixture end groups might be used to tailor boundary film properties instead of using physical mixtures of two or more PFPEs with different end groups. Lubricant transfer to the low-flying read/write head, head wear, and siloxane adsorption as a function of PFPE film thickness and of type are compared. Normalization of the data to the monolayer fraction instead of film thickness allows direct comparison between anisole- and hydroxyl-terminated PFPEs. Lubricant transfer to the head and head wear are independent of the functional end groups. Siloxane adsorption decreases with increasing anisole substitution of the hydroxyl groups. One-component PFPEs with mixed end groups provide a methodology by which boundary film properties could be adjusted.

Tunable Carbon Surface from Mono- to Multi-Metallic Single Atoms

2020 ◽  
Author(s):  
Weihong Lai ◽  
Heng Wang ◽  
Quan jiang ◽  
Zichao Yan ◽  
Hanwen Liu ◽  
...  
Keyword(s):  
Synergistic Effects ◽  
Structural Evolution ◽  
Charge Compensation ◽  
Catalytic Reactions ◽  
Single Atom ◽  
Carbon Surface ◽  
Hydrogen Electrode ◽  
Single Atoms ◽  
Mass Activity ◽  
Co Doped

<p>Herein, we develop a non-selective charge compensation strategy to prepare multi-single-atom doped carbon (MSAC) in which a sodium p-toluenesulfonate (PTS-Na) doped polypyrrole (S-PPy) polymer is designed to anchor discretionary mixtures of multiple metal cations, including iron (Fe<sup>3+</sup>), cobalt (Co<sup>3+</sup>), ruthenium (Ru<sup>3+</sup>), palladium (Pd<sup>2+</sup>), indium (In<sup>3+</sup>), iridium (Ir<sup>2+</sup>), and platinum (Pt<sup>2+</sup>) . As illustrated in Figure 1, the carbon surface can be tuned with different level of compositional complexities, including unary Pt<sub>1</sub>@NC, binary (MSAC-2, (PtFe)<sub>1</sub>@NC), ternary (MSAC-3, (PtFeIr)<sub>1</sub>@NC), quaternary (MSAC-4, (PtFeIrRu)<sub>1</sub>@NC), quinary (MSAC-5, (PtFeIrRuCo)<sub>1</sub>@NC), senary (MSAC-6, (PtFeIrRuCoPd)<sub>1</sub>@NC), and septenary (MSAC-7, (PtFeIrRuCoPdIn)<sub>1</sub>@NC) samples. The structural evolution of carbon surface dictates the activities of both ORR and HER. The senary MSAC-6 achieves the ORR mass activity of 18.1 A·mg<sub>metal</sub><sup>-1</sup> at 0.9 V (Vs reversible hydrogen electrode (RHE)) over 30K cycles, which is 164 times higher than that of commercial Pt/C. The quaternary MSAC-4 presented a comparable HER catalytic capability with that of Pt/C. These results indicate that the highly complexed carbon surface can enhance its ability over general electrochemical catalytic reactions. The mechanisms regarding of the ORR and HER activities of the alternated carbon surface are also theoretically and experimentally investigated in this work, showing that the synergistic effects amongst the co-doped atoms can activate or inactivate certain single-atom sites.</p>

2,2’-Dipyridylamine as Organic Molecular Electrocatalyst for Hydrogen Evolution Reaction in Acidic Electrolytes

2019 ◽  
Author(s):  
Xi Yin ◽  
Ling Lin ◽  
Hoon T. Chung ◽  
Ulises Martinez ◽  
Andrew M. Baker ◽  
...  
Keyword(s):  
Hydrogen Evolution ◽  
Hydrogen Evolution Reaction ◽  
Density Functional ◽  
Low Cost ◽  
Membrane Electrode Assembly ◽  
Carbon Surface ◽  
Membrane Electrode ◽  
Durability Test ◽  
Onset Potential ◽  
Precious Metal Catalysts

Finding a low-cost and stable electrocatalyst for hydrogen evolution reaction (HER) as a replacement for scarce and expensive precious metal catalysts has attracted significant interest from chemical and materials research communities. Here, we demonstrate an organic catalyst based on 2,2’-dipyridylamine (dpa) molecules adsorbed on carbon surface, which shows remarkable hydrogen evolution activity and performance durability in strongly acidic polymer electrolytes without involving any metal. The HER onset potential at dpa adsorbed on carbon has been found to be less than 50 mV in sulfuric acid and in a Nafion-based membrane electrode assembly (MEA). At the same time, this catalyst has shown no performance loss in a 60-hour durability test. The HER reaction mechanisms and the low onset overpotential in this system are revealed based on electrochemical study. Density functional theory (DFT) calculations suggest that the pyridyl-N functions as the active site for H adsorption with a free energy of -0.13 eV, in agreement with the unusually low onset overpotential for an organic molecular catalyst.<br>

2,2’-Dipyridylamine as Organic Molecular Electrocatalyst for Hydrogen Evolution Reaction in Acidic Electrolytes

2019 ◽  
Author(s):  
Xi Yin ◽  
Ling Lin ◽  
Hoon T. Chung ◽  
Ulises Martinez ◽  
Andrew M. Baker ◽  
...  
Keyword(s):  
Hydrogen Evolution ◽  
Hydrogen Evolution Reaction ◽  
Density Functional ◽  
Low Cost ◽  
Membrane Electrode Assembly ◽  
Carbon Surface ◽  
Membrane Electrode ◽  
Durability Test ◽  
Onset Potential ◽  
Precious Metal Catalysts

Finding a low-cost and stable electrocatalyst for hydrogen evolution reaction (HER) as a replacement for scarce and expensive precious metal catalysts has attracted significant interest from chemical and materials research communities. Here, we demonstrate an organic catalyst based on 2,2’-dipyridylamine (dpa) molecules adsorbed on carbon surface, which shows remarkable hydrogen evolution activity and performance durability in strongly acidic polymer electrolytes without involving any metal. The HER onset potential at dpa adsorbed on carbon has been found to be less than 50 mV in sulfuric acid and in a Nafion-based membrane electrode assembly (MEA). At the same time, this catalyst has shown no performance loss in a 60-hour durability test. The HER reaction mechanisms and the low onset overpotential in this system are revealed based on electrochemical study. Density functional theory (DFT) calculations suggest that the pyridyl-N functions as the active site for H adsorption with a free energy of -0.13 eV, in agreement with the unusually low onset overpotential for an organic molecular catalyst.<br>

Photoyellowing behavior of non-phenolic lignin models representative of end groups and β-ether structures

2004 ◽  
Vol 19 (2) ◽  
pp. 146-154
Author(s):  
Jim Parkås ◽  
Magnus Paulsson ◽  
Shiming Li ◽  
Knut Lundquist ◽  
Ulla Westermark
Keyword(s):  
End Groups

Carbon Surface Modification for Enhanced Corrosion Resistance

2008 ◽  
Author(s):  
P. M. Natishan ◽  
F. J. Martin ◽  
E. J. Lemieux ◽  
T. M. Newbauer ◽  
R. Rayne ◽  
...  
Keyword(s):  
Corrosion Resistance ◽  
Surface Modification ◽  
Carbon Surface

Synthesis, Characterization, and Dynamic Behavior of Well-defined Dithiomaleimide-functionalized Maltodextrins

2020 ◽  
Vol 17 (2) ◽  
pp. 85-89
Author(s):  
Francisco J. Hidalgo ◽  
Nathan A.P. Lorentz ◽  
TinTin B. Luu ◽  
Jonathan D. Tran ◽  
Praveen D. Wickremasinghe ◽  
...  
Keyword(s):  
Physicochemical Properties ◽  
Dynamic Behavior ◽  
Industrial Applications ◽  
19F Nmr ◽  
Nmr Studies ◽  
Synthetic Pathway ◽  
End Groups ◽  
Sugar End

: Maltodextrins have an increasing number of biomedical and industrial applications due to their attractive physicochemical properties such as biodegradability and biocompatibility. Herein, we describe the development of a synthetic pathway and characterization of thiol-responsive maltodextrin conjugates with dithiomaleimide linkages. 19F NMR studies were also conducted to demonstrate the exchange dynamics of the dithiomaleimide-functionalized sugar end groups.

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