Jiazeng Sun

High conductivity molten salts based on the imide ion

The bis(trifluoromethanesulfonyl)imide ion has recently been used in its lithium salt as a useful ion in solid polymer electrolytes because of the reduced degree of ion interaction its diffuse charge generates. In this work we have synthesised a number of novel salts based on the ammonium and pyrrolidinium cations of this anion. The salts all show reduced melting points compared with analogous halide salts. In some cases they are molten at room temperature. This latter group of salts have been characterized with respect to their properties as ionic liquids; the highest room temperature conductivity 2 mS cm−1 being exhibited by methyl butyl pyrrolidinium imide. Many of the salts are glass forming, exhibiting glass transition temperatures in the region of −90°C.

Cyto-toxicity and biocompatibility of a family of choline phosphate ionic liquids designed for pharmaceutical applications

Recently, the ionic liquid (IL) choline dihydrogen phosphate was demonstrated to improve the thermostability and shelf life of several model proteins, thus exhibiting potential as a stabilizing excipient or solvent for protein therapeutics. Before novel ILs can be used for biomedical applications, comprehensive data is required to establish biocompatibility, including cytotoxicity effects and solution behavior. In this study five phosphate-based anion moieties were analyzed: H2PO4− (DHP), dibutyl phosphate (DBP), bis(2-ethylhexyl) phosphate (BEH), bis(2,4,4-trimethylpentyl) phosphinate (TMP), and O,O′-diethyl dithiophosphate (DEP), all paired with the cation choline (C). Toxicity levels for these ILs, and a common sugar and salts, were established using a J774 murine macrophage cell line. The sugar trehalose, and the simple salts sodium chloride and choline chloride yielded EC50 values of >100, 63 and 34 mM, respectively. The EC50 values (mM) of CDHP (20), CDBP (9.1), and CDEP (8.2) were lower than, but within the range of simple salts NaCl (62.8) and choline Cl (33.7). The EC50 values of CTMP and CBEH were considerably lower, 0.25 and 0.30 mM, respectively. CDHP and CBEH displayed a hormetic response. Osmolality measurements indicated that CDHP, CDBP, and CDEP exhibit nearly complete dissociation in aqueous solution, with osmotic coefficients of 1.0, 0.9, and 0.8, whereas CTMP and CBEH have coefficients of 0.5 and 0.3, and are more molecular in character. A high correlation between the EC50 value and the anion mass fraction indicated that anion size and the presence of moderately long and/or branched alkyl chains may affect viability.

Solid state actuators based on polypyrrole and polymer-in-ionic liquid electrolytes

Novel polymer-in-ionic liquid electrolytes (PILEs) have been developed for solid state electrochemical actuators based on polypyrrole. The active polymer electrodes are readily oxidized/reduced without degradation in the PILE. It was found that the actuator cycle life is significantly enhanced in the PILE as is the ‘shelf life’ of the device.

Acid–organic base swollen polymer membranes

In this work, two different polymer membrane systems based on Nafion and Teflon were investigated as proton conductors for polymer membrane fuel cells. Water-free Nafion117 membranes swollen with different non-aqueous solvents were prepared. The solvents included imidazole, imidazole–imidazolium salt solutions, room temperature molten salts and molten salt–acid solutions. Teflon films were treated with a surfactant, or a Nafion solution, to improve their surface properties, and were subsequently swollen with phosphoric acid. Conductivity measurements were carried out on both the Nafion and Teflon membranes. Conductivities in the range of 10−3 S cm−1 at around 100°C were obtained. This is still an order of magnitude lower than the corresponding water swollen Nafion at 80°C.

Structure-property relationships in plasticized solid polymer electrolytes

The addition of various kinds of plasticizers can enhance the conductivity of polymer electrolyte systems, in some cases by many orders of magnitude. The plasticizer may be a low molecular weight solvent, or be a low molecular weight polymer. As the plasticizer concentration increases there is an inevitable deterioration in material properties. In this work we have investigated the effect of plasticizer on the conductivity, thermal properties and matrial properties of a number of systems including urethane cross-linked polyethers and polyacrylates. In some of the systems, in particular the polyether electrolytes, the plasticizer acts to enhance conduction by acting as a cosolvent for the salt as well as increasing chain flexibility. Its efficacy is dependent on its structure and characteristics as a solvent. Although Tg is lowered in a close to linear fashion with increasing plasticizer content and thereby conductivity increased rapidly, the elastic modulus changes more slowly. This reflects the coupling of conduction to the local mobility of the molecular units of the combined solvent system and the relative decoupling of the mobility and glass transition from the material properties. In these systems the latter are a function mainly of the longer range structure of the polymer network. The changes in conductivity and materials properties are interpreted in terms of a configurational entropy model of the solution.

Ionic Liquids as Antiwear Additives in Base Oils: Influence of Structure on Miscibility and Antiwear Performance for Steel on Aluminum

The use of ionic liquids as additives to base oil for the lubrication of steel on aluminum was investigated. The miscibility and wear performance of various phosphonium, imidazolium, and pyrrolidinium ionic liquids in a range of polar and nonpolar base oils was determined. The structure and ion pairing of the ionic liquids was found to be important in determining their miscibility in the base oils. In wear tests, some of the miscible base oil/IL blends reduced the aluminum wear depth when compared to that found with the base oil alone. The nonpolar base oil/IL blends were able to withstand higher wear-test loads than the polar base oil/IL blends. At 10 N, as little as 0.01 mol/kg of IL, or 0.7-0.9 wt %, in the nonpolar base oils was enough to drastically reduce the wear depth on the aluminum. XPS analysis of the wear surfaces suggested that the adsorbing of the IL to the surface, where it can form low-shear layers and also react to form tribofilms, is important in reducing friction and wear. The largest reductions in wear at the highest load tested were found for a mineral oil/P6,6,6,14 (i)(C8)2PO2 blend.

Synthesis and properties of ambient temperature molten salts based on the quaternary ammonium ion

The synthesis of 16 tetraalkyl ammonium bis(trifluoromethane sulfonyl) imide salts, are reported in this paper. Trends in properties of these salts are discussed. The symmetrical tetraalkyl ammonium salts with the bis(trifluoromethyl sulfonyl) imide anion exhibited a lower melting point than that of corresponding ammonium halides. The salts with low symmetry ammonium cations were found to be of generally lower melting point, and many were stable liquids at room temperature. Several of these did not crystallize during cooling below room temperature and exhibited glass transition temperatures in the region of −60 °C∼−80 °C. A comparison of properties between the ammonium imide salts and corresponding trifluoromethane sulfonates is also presented.

Polymer-in-ionic-liquid electrolytes

In order to achieve high conductivity in a polymer electrolyte, polymer-in-ionic-liquid electrolytes have been explored. It is found in this study that poly-[vinylpyrrolidone-co-(vinyl acetate)] (P(VP-c-VA) in 1-ethyk-3-methylimidazolium bis(trifluoromethyl sulfonyl) amide (EtMeIm + Tf2N - ) and poly(N,N-dimethyl acrylamide) (PDMAA) in trimethyl butyl ammonium bis(trifluoromethane sulfonyl) amide (N + 1114 Tf 2 N - ) produce ion-conducting liquids and gels. The P(VP-c-VA)/ EtMeIm + Tf 2 N - mixture has a conductivity around 10 -3 S . cm -1 at 22°C, for copolymer concentrations up to 30 wt.-%. Thermal analysis shows that the Tg of the PVP(VP-c-VA)/ EtMeIm + Tf 2 N - system is well described by the Fox equation as a function of polymer content. Poly(methyl methacrylate) (PMMA)/ EtMeIm + Tf 2 N - gel electrolytes were prepared by in-situ polymerisation of the monomer in the ionic liquid. In the presence of 0.5 - 2.0 wt.-% of a crosslinking agent, these PMMA-based electrolytes displayed elastromeric properties and high conductivity (ca. 10 -3 S. cm -1 ) at room temperature.

Lithium polyelectrolyte–ionic liquid systems

Novel lithium polyelectrolyte–ionic liquid systems, using poly(lithium 2-acrylamido-2-methyl propanesulfonate) and its copolymer with N-vinyl formamide, have been developed in this work. The ionic liquid used in this work is from a novel family of methanesulfonate ionic liquids, specifically N-hexyl-N,N,N-tributyl ammonium methanesulfonate, which is chosen because of the similarity with the anionic functionality of the polymer. The ionic liquid thereby acts as a good solvating medium for the polyelectrolyte. It was found that the copolymer-based polyelectrolyte–ionic liquid system exhibits two to three times higher conductivity than that of the homopolymer system. The results of solid-state 7Li-NMR have shown that lithium cations in the copolymer system are mobile whereas in the homopolymer, only a fraction appears to be mobile even at 80 °C. This supports the hypothesis that separation of the charged groups on the polymer backbone via the co-monomer encourages the dissociation of lithium cations from the sulfonate groups bonded to the polymer chains, and hence, results in an increase in conductivity of the polyelectrolyte material.

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 (NTf(2)) anion containing ILs. However, in the case of the FAP and NTf(2) based systems, a cation dependence was observed, with relatively poor wear resistance obtained in the case of an imidazolium FAP and two pyrrolidinium NTf(2) 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.