Novel high salt content polymer electrolytes based on high Tg polymers

Conductivities greater than or equal to 10⁻⁸ S cm⁻¹ at T_g are reported in polymer electrolytes based on lithium triflate salt and a series of polymers whose T_g is greater than 90°C. The highest conductivities were observed for poly(acrylonitrile) based systems with salt concentrations greater than 60 wt.%. The conductivity in all cases investigated increases with increasing salt concentration. ¹H-NMR T₂ relaxation measurements suggest that T_g decreases with increasing salt content and confirms that these materials are glassy at room temperature and hence that the conductivity is significantly decoupled from the structural relaxations. It appears that the nature of the polymer is important in determining the level of ionic conductivity, possibly due to differences in polymer coordinating ability or differences in T_g. Polymer-in-salt mixtures based on a tetra-alkyl ammonium imide molten salt and several high T_g polymers are also reported. The conductivities of these mixtures appear to be independent of the polymer type.

13 C NMR spin–lattice relaxation times as a probeof local polymer dynamics in plasticized polyethers

¹³C NMR spin–lattice relaxation times T₁ are used to investigate the effect of low molecular weight diluents, including N,N-dimethylformamide, N-methylformamide, propylene carbonate, γ-butyrolactone, triglyme and tetraglyme, on the local polymer segmental motion in polyether–urethane networks. In all cases, an increase in the local mobility is deduced from the increasing T₁ measurements consistent with a decreasing glass transition temperature. The extent of plasticization, however, is dependent on the nature of the small molecules. Those molecules which can either form strong polymer-diluent interactions (for example through dipolar interactions) or are themselves rigid, give the least enhancement of polymer mobility and the greatest deviation from the Fox equation for T_g. In the presence of alkali metal salts, N,N-dimethylformamide and propylene carbonate are shown to have opposite effects on the local polymer motion, as seen from the T₁ measurements. In both cases, addition of the plasticizers increases the ¹³C T₁ relaxation times for the plasticizer. However, propylene carbonate decreases the polymer ¹³C T₁ whilst N,N-dimethylformamide results in the expected increase in polymer ¹³C T₁.

Towards a better understanding of 'delocalized charge' in ionic liquid anions

One of the main characteristics that are attributed to ionic liquids (especially those with a low melting point) is that the anions comprising the ionic liquids possess a certain degree of charge delocalization as compared to anions in traditional molten salts. Based on the proton affinity equilibrium we proposed a new energetic criterion that can be used as a measure of charge delocalization. The proposed proton affinity comparison quantifies the extent to which ionic liquid anions are delocalized. Thus it should lead to a better understanding towards the design of task-specific ionic liquids. Therefore, this criterion can be applied to newly designed anions to assure that the extent of charge delocalization falls within the same range of values on the proton affinity scale as other commonly used ionic liquid anions.

Fast ion conduction in molecular plastic crystals

Doping of lithium salts and acids into the plastic crystal phase of succinonitrile has shown for the first time of the possibility of creating solid state electrolytes based on plastic crystalline solvents where the matrix itself is neutral and hence not intrinsically conductive. These materials illustrate the concept of a solid state electrolyte solvent. Room temperature conductivities up to 3.4×10⁻⁴ S cm⁻¹ were obtained with 5 wt.% lithium bis(trifluoromethanesulfonylamide) in succinonitrile. Pulsed field gradient NMR measurements indicate that both cation and anion are mobile in this lattice. Proton conductivity was also observed when methane sulfonic acid or glacial acetic acid was used as dopants, however, the conductivity in these systems is limited by the poor dissociating ability of these acids.

Ionic conduction in doped succinonitrile

Doping of lithium salts into the plastic crystal phase of succinonitrile does significantly increase ionic conductivity. This paper investigates the effect of anion (TFSA, Tf and BF₄) on the conductivity and diffusion of the mobile species using impedance spectroscopy and NMR. Room temperature conductivities up to 2.1×10⁻⁴ S cm⁻¹ were obtained with 1 mol% lithium bis(trifluoromethanesulfonyl)amide in succinonitrile. Pulse field gradient NMR has shown that in all three systems investigated, both cation and anion are mobile in this lattice.

Dynamic mechanical thermal analysis studies of factors influencing relaxation in polyetherurethane based solid electrolytes

Dynamic mechanical thermal analysis (DMTA) has been used to study the effects of plasticizers on the mobility and homogeneity of a series of solid polymer electrolytes (SPEs). With reference to previously published results on similar systems containing LiClO₄ salts and tetraglyme as plasticizer, the effects of propylene carbonate (PC) on the glass transition temperature (T_g) of the SPE and on the distribution of relaxation times within the sample are discussed; at low plasticizer concentration PC has little effect on T_g as measured by DMTA in comparison with tetraglyme, and at higher plasticizer concentrations PC significantly broadens the mechanical relaxation behaviour indicating a greater degree of dynamical heterogeneity within the sample. A second low temperature relaxation is evident at lower PC contents indicating that some regions of this plasticized SPE are distinctly more mobile than others or perhaps, on this length scale, that some degree of phase separation is present. Activation energies for the mechanical relaxation were also determined as a function of PC concentration and are significantly greater than those determined from conductivity measurements.

One-step synthesis of conducting polymer–noble metal nanoparticle composites using an ionic liquid

Conducting polymers containing incorporated gold or silver nanoparticles have been synthesized using ionic liquid solutions of gold chloride or silver nitrate. Use of the metal salts as the oxidant for monomers such as pyrrole and terthiophene allows the composites to be formed in one simple step, without the need for templates or capping agents. The incorporated metal nanoparticles are clearly visible by TEM, and the composites have been further analyzed by TGA, CV, UV-Vis, Raman, XPS and scanning TEM coupled with EDS analysis. Utilization of an ionic liquid allows the full oxidizing power of the gold chloride to be accessed, resulting in incorporation of metallic gold into the polymers.

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.

A new family of ionic liquids based on the 1-alkyl-2-methyl pyrrolinium cation

Five new salts based on 1-alkyl-2-methyl pyrrolinium ion are reported, two involving the iodide ion and three involving the bis(trifluoromethanesulfonyl) amide ion. The iodide salts have melting points around 100 °C, while the amide salts have melting points around room temperature. Two of the amide salts can be easily quenched into the glassy state and exhibit glass transition temperatures around −70 °C. The 2-methyl pyrrolinium cation bears structural similarities to the aromatic imidazolium cations on one hand and the cyclic ammonium cation family based on the pyrrolidinium cation on the other. The properties of the salts reported here are compared within these two related families of salts.

Control of magnesium interfacial reactions in aqueous electrolytes towards a biocompatible battery

A stable magnesium battery has been developed based on a magnesium anode, a poly(dioxyethane thiophene) (PEDOT) cathode and a near-saturated aqueous solution of LiCl, MgCl₂, or mixture of these salts at pH of 11. This combination leads to a low water activity in the electrolyte, which thus suppresses the hydrogen evolution reaction on Mg, as well as producing a stable oxy-hydroxide film which protects the metal surface from freely corroding. The conducting polymer cathode is reduced somewhat during the discharge process, however, appears to be readily re-oxidised (as determined from the resistance) by the oxygen present in the cell. The cell is therefore primarily a Mg/O₂ battery, however, the PEDOT appears to enhance the performance, in particular the discharge voltage.

Novel Lewis-base ionic liquids replacing typical anions

We have synthesized two kinds of new Lewis-base ionic liquids (ILs); one is based on the relatively strong Lewis basic acetate anion, and the other is a salt composed of a mono-alkylated diamine such that the Lewis base site is incorporated in the cation. 1-Octyl-4-aza-1-azonia-bicyclo[2.2.2]octane bis(trifluoromethanesulfonyl)amide, [C₈dabco]TFSA, and N-butyl-N-methylpyrrolidinium acetate, [p_1,4]OAc, melted into fluid liquids at 26 and 81 °C, respectively. The thermal decomposition of [p_1,4]OAc started at around 150 °C, whereas the thermal stability of [C₈dabco]TFSA was almost equal to that of typical TFSA-based ILs in spite of the Lewis base site. This suggests that if the Lewis base site is incorporated into the cation the IL can maintain higher thermal stability. In addition, as a further result of the presence of the basic nitrogen, [C₈dabco]TFSA can dissolve hydrated Cu(NO₃)₂ whereas the other TFSA-based ILs cannot.

Autocatalytic nature of permanganate oxidations exploited for highly sensitive chemiluminescence detection

Manganese(II) salts catalyze the chemiluminescent oxidation of organic compounds with acidic potassium permanganate. The formation of insoluble manganese(IV) species from the reaction between manganese(II) and permanganate can be prevented with sodium polyphosphate, and therefore, relatively high concentrations of the catalyst can be added to the reagent before the lightproducing reaction is initiated. The rapid and intense emissions from these manganese(II) catalyzed chemiluminescence reactions provide highly sensitive detection and greater compatibility with liquid chromatography.

Impact of secondary salinisation on freshwater ecosystems : effect of experimentally increased salinity on an intermittent floodplain wetland

Intermittent wetlands are particularly at risk from secondary salinisation because salts are concentrated during drawdown. We conducted a field experiment to examine the effect of adding salt at two different concentrations (to achieve nominal conductivities of 1000 μS cm–1 (low salt) and 3000 μS cm–1 (high salt)) on water quality, freshwater plants and epiphytic diatoms in an intermittent wetland during a 3.3-month drawdown. Conductivity increased to 3000 and 8500 μS cm–1 in low-salt and high-salt treatments respectively. Salt was apparently lost to the sediments, causing protons to be released from the sediments and reducing water column pH from 6.9 to 5.5 in the low-salt treatment and to 4.0 in the high-salt treatments. Forty days after adding the salt, biomass, %cover and flower production in Potamogeton cheesmanii were significantly reduced, whereas Amphibromus fluitans was not significantly affected. The salt effect on Triglochin procera was intermediate between the other two macrophytes. Significant reductions in the density, species richness and diversity of epiphytic diatoms occurred in the high-salt, but not in the low-salt, treatments. Our work shows that increases in salinity, and thus conductivity (up to 8500 μS cm–1), in low-alkalinity intermittent wetlands can change water quality, with significant adverse effects on some macrophyte and diatom communities.

Analysis of self-assembled monolayer interfaces by electrospray mass spectrometry : a gentle approach

A general mass spectrometry technique for the characterization of alkanethiol-modified surfaces is presented. Alkanethiol self-assembled onto a gold surface (in this case, peptides were attached to the gold surface via a thiolate bond) was reductively desorbed in 0.05 M KOH in the presence of octadecyl-derivatized silica gel. The peptide adsorbed onto the silica gel, whereupon it could be filtered, washed to remove any salts, and then eluted using a mixture of 4:1 v/v methanol/water. The eluant containing the peptide was injected into a Fourier transform ion-cyclotron resonance mass spectrometer (FTICR/MS) via electrospray ionization. The spectrum showed no fragmentation of the peptide, demonstrating the gentleness of the technique. This simple procedure is not limited to FTICR/MS and could be adapted to other mass spectrometers.