A comparison of phosphorus and fluorine containing IL lubricants for steel on aluminium

Ionic liquids have been shown to be highly effective lubricants for a steel on aluminium system. This work shows that the chemistry of the anion and cation are critical in achieving maximum wear protection. The performance of the ILs containing a diphenylphosphate (DPP) anion all showed low wear, as did some of the tris(pentafluoroethyl)trifluorophosphate (FAP) and bis(trifluoromethanesulfonyl)amide (NTf2) anion containing ILs. However, in the case of the FAP and NTf2 based systems, a cation dependence was observed, with relatively poor wear resistance obtained in the case of an imidazolium FAP and two pyrrolidinium NTf2 salts, probably due to tribocorrosion caused by the fluorine reaction with the aluminium substrate. The systems exhibiting poor performance generally had a lower viscosity, which also impacts on their tribological properties. Those ILs that exhibited low wear were shown to have formed protective tribofilms on the aluminium alloy surface.

Fluorine-free superhydrophobic coatings with pH-induced wettability transition for controllable oil-water separation

We present a simple, environmentally friendly approach to fabricating superhydrophobic coatings with pH-induced wettability transition. The coatings are prepared from a mixture of silica nanoparticles and decanoic acid-modified TiO2. When the coating is applied on cotton fabric, the fabric turns superhydrophobic in air but superoleophilic in neutral aqueous environment. It is permeable to oil fluids but impermeable to water. However, when the coated fabric is placed in basic aqueous solution or ammonia vapor, it turns hydrophilic but underwater superoleophobic, thus allowing water to penetrate through but blocking oil. Therefore, such a unique, selective water/oil permeation feature makes the treated fabric have capability to separate either oil or water from a water-oil mixture. It may be useful for development of smart oil-water separators, microfluidic valves, and lab-on-a-chip devices.

Synthesis and molecular structure of [n-Bu2(F)SnOSn(F)t-Bu2]2 - an unsymmetrically substituted tetraorganodistannoxane

The dimeric tetraorganodistannoxane [n-Bu₂(F)SnOSn(F)t-Bu₂]₂ (1) was prepared by the reaction of (t-Bu₂SnO)₃ with n-Bu₂SnF₂ and characterized in solution by multinuclear NMR spectroscopy and ESI MS spectrometry and in the solid state by ¹¹⁹Sn MAS NMR spectroscopy and single crystal X-ray diffraction.

The first dimeric trioganotin fluoride : stabilization by unsymmetrically oriented menthyl substituents

In the solid state, (-)-tris([1R,2S,5R]-menthyl)tin fluoride, Men₃SnF (6), exhibits a dimeric structure in which one tin atom is four-coordinate and the other five-coordinate. This novel dimeric association mode is attributed to the orientation of the unsymmetrical menthyl groups, which are arranged to allow a minimum Sn···Sn separation of 4.84 Å within the dimer. The exocyclic isopropyl groups of the menthyl groups point in opposite directions on each tin atom of the dimer, thus preventing further association (Sn···Sn separation outside the dimer 10.49 Å). ¹¹⁹Sn and ¹⁹F MAS NMR spectroscopy were utilized to probe the diverse coordination numbers found by X-ray crystallography for the geometries of the two tin and fluorine sites. In solution, 6 is a monomer at both room temperature and -100 °C. However, upon addition of Bu₄NF, 6 is in equilibrium with [(Men₃SnF)₂F]- (6a), [Men₃SnF₂]^- (6b), and noncoordinating fluoride anions.

Chemiluminescence : gas-phase

Article Outline
• Introduction
• Chemiluminescence of Nitrogen Compounds
• Thermal Energy Analyzer
• Nitrogen-Selective Detector
• Redox Chemiluminescence Detection
• Chemiluminescence of Sulfur Compounds
• Chemiluminescence of Hydrocarbons
• Other Reactions with Ozone
• Flame Photometric Detector
• Other Reagent Gases
• Molecular Fluorine<br />• Atomic Fluorine<br />• Atomic Oxygen
• Active Nitrogen
• Atomic Sodium
• Chlorine Dioxide
• Official Methods
• Further Reading

Studies of hypervalent organotin complexes and organotin clusters

(119)Sn, (31)P and (13)C variable temperature NMR spectroscopies have been used to examine the effective coordination spheres in solution of a series of hypervalent organotin(IV) dithiolate compounds RnSnXm(S-S)4-n-m where R = Ph, Me, nBu, tBu; X = Cl, Br; (S-S) = S2CNR'2, S2COR', S2P(OR')2 (R' = Me, Et, iPr) and n = 1, 2, 3; m = 0,1,2. Stereochemical nonrigidity is a common phenomenon found for these hypervalent compounds. On the basis of heteronuclear NMR data and X-ray crystallographic data, dynamic behaviors of these hypervalent compounds have been established. The system of hypervalent organotin(IV) fluoride complexes has also been investigated by variable temperature heteronuclear NMR techniques. A series of monomeric pentacoordinate complexes [RnSnC1mF5-n-m]-(R = Ph, Me, nBu, tBu; n = 2, 3; m - 0, 1, 2, 3) and dimeric complexes [(Me3SnX)F(Me3SnX')]- (X = F, Cl; X' = F, Cl) and hexacoordinate complexes [RnSnClmF6-n.m]2- (R = Ph, Me, nBu; n = 1, 2; m = (X 1, 2, 3,4) are identified in solution. The fluoride is of higer affinite to tin than the chloride. The stereochemistry and dynamic behavior of these complexes in solution has been studied. Fluoride ion may induce phenyl group disproportionation of phenyhin(IV) compounds. It is also found that in pentacoordinate diorganotin complexes, such as [Ph2SnCl2F]- and [Ph2SnClF2]- fluorine can be less apicophilic than chlorine. Studies of stereochemistry and dynamic behavior of bi-functional Lewis acid bis(haloorganosiannes) have also been carried out. The bis(haloorganostannes) exhibit strong chelate ability towards halide, with high selectivity on fluoride, forming heterocyclic chelating rings, the stability of which depend on the ring size. In further exploration of the Lewis acidity of organotin(IV) halides, complexation of organotin(IV) halides with bis(tertiary phosphinc) ligands has been studied by 119Sn and 31P NMR spectroscopy and X-ray crystallography. The phenyl group disproportionation is often observed in the complexation reaction. Furthermore, organotin(IV) clusters such as [(RSn)12O14(OH)6]Cl2-2H2O (R = iPr, nBu) have been successfully prepared by base hydrolysis of RSnCl3. These clusters contain 12 tin atoms in one molecule and the cores of the clusters are dications. Other organotin clusters such as [nBuSn(O)O2CCH3]6 and [(nBuSn(OH)O2PPh2)3][O2PPh2) are readily formed by reaction of the 12-tin-atom cluster with an appropriate acid. The reactivity of and interconversion between organotin(FV) clusters have also been studied.

A 7Li and 19F NMR relaxation study of LiCF3SO3 in plasticised solid polyether electrolytes

⁷Li and ¹⁹F NMR relaxation time (T₁, T₂, T_1ρ) measurements have been used to probe the dynamics of LiCF₃SO₃ dissolved in an amorphous co-polymer poly(ethylene oxide-co-propylene oxide), and in particular the influence of the plasticising agents propylene carbonate and dimethyl formamide. The changes in relaxation behaviour of ¹⁹F and ⁷Li with increasing plasticiser concentration are very different, as is the effect of each plasticiser. These differences can be explained qualitatively in terms of the interaction between the plasticiser and the ions. Preliminary ⁷Li T_1ρ measurements reveal two components at low temperatures.

Conductivity and NMR properties of plasticized polyethers complexed with lithium salts

NMR provides a tool whereby the dynamic properties of specific nuclei can be investigated. In the present study, a poly(ethylene oxide-co-propylene oxide) network has been used as the polymer host to prepare solid polymer electrolytes (SPE) containing either LiClO₄ or LiCF₃SO₃. In addition, a low molecular weight plasticizer [propylene carbonate (PC), dimethyl formamide (DMF) or tetraglyme] has been added to several of the samples to enhance the mobility of the polymer and, thus, of the ionic species. The effects of plasticizer and salt concentration on the ionic structure and mobility in these SPEs, as measured by NMR relaxation times, and correlation to the conductivity behaviour in these systems are discussed. Temperature dependent triflate diffusion coefficients, as measured by Pulsed Field Gradient ¹⁹F-NMR, in plasticized SPEs are also reported.

An nmr investigation of ionic structure and mobility in plasticized solid polymer electrolytes

²³Na and ¹⁹F nuclear magnetic resonance spectroscopy is used to investigate the effect of plasticizer addition on ionic structure and mobility in a urethane crosslinked polyether solid polymer electrolyte. The incorporation of dimethyl formamide and propylene carbonate plasticizers in a sodium triflate/polyether system results in an upfield chemical shift for the ²³Na resonance consistent with decreased anion-cation association and increased cation-plasticizer interactions. The ¹⁹F resonances appears less susceptible to changes in chemical environment with only minor chemical shift changes recorded. Spin lattice relaxation measurements for the ¹⁹F nucleus are also reported. Two minima are observed in the relaxation measurements consistent with both an inter and intramolecular relaxation mechanism.

Solid state NMR characterization of polyrrole : the nature of the dopant in PF6− doped films

³¹P and ¹⁹F solid state NMR have been used to study the nature of the PF₆− anion in polypyrrole films at various levels of oxidation. It appears that the symmetric PF₆− unit remains undistorted and unchanged throughout, suggesting that it is predominantly acting only as a counterion and not as a true ‘dopant’, since any distortion in the phosphorous environments would result at the very least in chemical shift anisotropy of the ³¹P nucleus. A second set of phosphorous and fluorine resonances, which are consistent with a difluoride phosphorous compound, appeared in the films. Upon electrochemical reduction of the polymer, the undistorted PF₆− anion leaves the film whereas the second phosphorous species remains. Re-oxidation of the polymer reverses the processes observed during reduction.

Solid state NMR analysis of polypyrrole grown in a phosphonium ionic liquid

³¹P, ¹⁹F and ¹³C solid state NMR analysis has been used to investigate the intercalation/de-intercalation of both anions and cations in electrochemically synthesized polypyrrole films. Use of a phosphonium-based ionic liquid, tri(hexyl)(tetradecyl)phosphonium bis(trifluoromethanesulfonyl)amide, allows the separate detection of the cation and anion by analysis of the phosphorous and fluorine resonances, respectively. Initial results indicate the incorporation of both cations and anions during film growth in the ionic liquid. There is a notable change in the ³¹P chemical shift of the cation on incorporation into the film, consistent with a significant change in environment compared to the pure ionic liquid. Despite its large size, the phosphonium cation can be completely expelled from the film by oxidation.

On the role of cyclic unsaturated additives on the behaviour of lithium metal electrodes in ionic liquid electrolytes

Three cyclic vinyl based additives, based respectively on oxygen, sulphur and fluorine, are tested for their ability to improve the cycling of lithium in a hostile ionic liquid medium. Oxygen based vinylene carbonate is found to offer the best protection of the lithium metal whilst allowing very consistent lithium cycling to occur. The vinylene carbonate based system under study is, however, imperfect. Lithium metal is deposited in a dendritic morphology, and vinylene carbonate is rapidly consumed during lithium cycling if it is present in a small quantity. Our results suggest that ionic liquid systems critically relying on a small amount of additive to protect a lithium electrode are not viable for long cycle life secondary batteries. It is suggested that an ionic liquid which itself is lithium metal compatible be used instead.

Phosphonium ionic liquids as lubricants for aluminium-steel

The performance of a series of novel room temperature ionic liquids (ILs) based on the trihexyl(tetradecyl)phosphoniumcation (P66614 +) and a number of novel anions have been studied in pin-on-disk tests using a 100Cr6 steel ball on AA2024 aluminium disks.

The anions coupled to the (P66614 +) cation include diphenyl phosphate (DPP-), dibutyl phosphate (DBP-), bis (2,4,4-trimethyl pentyl) phosphinate (M3PPh-) and bis(2-ethyl hexyl) phosphate (BEH-).

More traditional anions such as bis(trifluoromethanesulfonyl) amide (NTf2 -) and bromide (Br-) were also investigated. Experiments were conducted at various loads to assess the IL film forming abilities.

The results suggest that the structure of the anion is important in forming a surface film that reduces the friction and wear of the aluminium disk. At 30N five of the six ILs tested showed a 30-90% reduction in wear, as determined from wear scar depth measurements, compared to fully formulated diesel oil.

The IL lubricant with a diphenyl phosphate anion achieved the lowest wear coefficient, showing a better performance than a typical fluorine-containing IL anion, NTf2.

To further investigate wear mechanisms and surface interactions the wear scars were analysed using a scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS).

A review of ionic liquid lubricants

Due to ever increasing demands on lubricants, such as increased service intervals, reduced volumes and reduced emissions, there is a need to develop new lubricants and improved wear additives. Ionic liquids (ILs) are room temperature molten salts that have recently been shown to offer many advantages in this area. The application of ILs as lubricants in a diverse range of systems has found that these materials can show remarkable protection against wear and significantly reduce friction in the neat state. Recently, some researchers have shown that a small family of ILs can also be incorporated into non-polar base oils, replacing traditional anti-wear additives, with excellent performance of the neat IL being maintained. ILs consist of large asymmetrical ions that may readily adsorb onto a metal surface and produce a thin, protective film under boundary lubrication conditions. Under extreme pressure conditions, certain IL compounds can also react to form a protective tribofilm, in particular when fluorine, phosphorus or boron atoms are present in the constituent ions.

A novel approach to functionalise pristine unsized carbon fibre using in situ generated diazonium species to enhance interfacial shear strength

Complex molecules have been successfully grafted onto the surface of unsized carbon fibre, a heterogeneous material which is a challenge to functionalise. The in situ generation of highly reactive phenyldiazo-species from their corresponding anilines was employed to achieve this task. The success of an initial proof-of-concept study (bearing a nitro moiety) supported by X-ray Photoelectron Spectroscopy (XPS) and physical characterisation, led to the design and synthesis of a more complex compound possessing a pendant amine moiety which could theoretically react with an epoxide based resin. After attachment to unsized oxidised fibres, analysis by XPS of the resulting fibres (fluorine used as an XPS tag) indicated a marked difference in functionalisation success which was attributed to steric factors, shown to be critical in influencing the attachment of the phenyldiazo-intermediate to the carbon fibre surface. Analysis of key fibre performance parameters of these fibres showed no change in elastic modulus, strength, surface topography or microscopic roughness when compared to the control unsized oxidised fibres. The functionalised fibres did however show a large increase in coefficient of friction. Single fibre fragmentation tests indicated a marked increase in interfacial shear strength, which was attributed to the pendent amine functionalities interacting with the epoxy resin.