Ionic Liquid Uptake Research Articles

Phosphonium and Ammonium Ionic Liquids with Aromatic Anions: Synthesis, Properties, and Platinum Extraction

Several hydrophobic long-chain quaternary ammonium and phosphonium ionic liquids (ILs) with functionalized aromatic anions were prepared following a metathesis route using tricaprylmethylammonium chloride (Aliquat 336) and trihexyl(tetradecyl)phosphonium chloride (Cyphos IL101) as precursors. The incorporation of aromatic anions bearing hydroxy-, methoxy-, thiol-, and thioether functionalities as well as tetraphenylborate anions resulted in an increased chemical stability of the ILs and an alteration of their physico-chemical properties. Furthermore, aromatic anions significantly decreased the water solubility and water uptake of both ammonium and phosphonium-based ILs. Thiol- and thioether ILs were applied for the extraction of platinum from aqueous phase using liquid phase micro-extraction. Time dependent studies showed a rapid elimination of up to 95% platinum after 30 min. With a leaching of the anion <0.01 wt-% into the aqueous media, the evaluated ILs were found to be suitable as extracting agents for platinum from aqueous solutions.

Effect of Ionic Liquid on Mechanical Properties and Morphology of Zwitterionic Copolymer Membranes

Zwitterionomers containing less than 13 mol % zwitterion functionality were synthesized using free radical copolymerization of n-butyl acrylate (nBA) and sulfobetaine monomers. X-ray scattering results revealed a two-phase morphology, which is typical of random ionomers with an ionomer peak at q ∼1.5 nm−1. Swelling studies in the ionic liquid (IL), 1-ethyl-3-methylimidazolium ethylsulfate (EMIm ES), showed an influence of zwitterionic structure on IL uptake. Zwitterionomer membranes were swollen to various IL contents, and the influence of IL on mechanical properties, morphology, and ionic conductivity was explored through dynamic mechanical analysis (DMA), X-ray scattering, and impedance spectroscopy, respectively. Results revealed that IL preferentially swelled the zwitterionic domains but was excluded from the matrix phase. Significant changes in mechanical properties and ionic conductivity were observed above a critical uptake of IL. Fundamental explorations of the interaction of ILs with sulfobetaine-containing copolymers may lead to the use of zwitterionomers in emerging membrane applications.

Interfacial Interactions in Aprotic Ionic Liquid Based Protonic Membrane and Its Correlation with High Temperature Conductivity and Thermal Properties

Novel supported liquid membranes (SLMs) have been developed by impregnating Nafion and Hyflon membranes with ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMI-BTSI). These supported liquid membranes were characterized in terms of their ionic liquid uptake behavior, leaching of ionic liquid by water, thermal stability, mechanical properties, glass transition temperature, ion exchange capacity, and proton conductivity. In general, modified membranes are more flexible than unmodified samples due to the plasticization effects of the ionic liquid. However, these supported liquid membranes exhibit a significant increase in their operational stability and proton conductivity over unmodified membranes. We also demonstrate that proton conductivity of these supported liquid membranes allows conduction of protons in anhydrous conditions with conductivity increasing with temperature. Conductivity of up to 3.58 mS cm(-1) has been achieved at 160 degrees C in dry conditions, making these materials promising for various electrochemical applications.

The role of water in transport of ionic liquids in polymeric artificial muscle actuators

Ionic liquid (IL) based polymeric mechanical actuators show promise for providing an important and unprecedented combination of electromechanical and soft material properties. Measurement of ion transport in an ionomer/IL membrane is essential for understanding and designing these “artificial muscle” actuators. Furthermore, water forms a ubiquitous part of these hydrophilic membrane systems when used in open air, greatly affecting electrochemical and physical properties including the ion conductivity critical for actuation performance. Here we present the first study quantifying the delicate interplay between water and an IL absorbed in an ionomer membrane as used in ionic polymer actuators. We use 1H and 19F NMR diffusometry to investigate cation and anion diffusion of 1-ethyl-3-methyl-imidazolium trifluoromethanesulfonate (EMI-Tf), swollen into a perfluorosulfonate ionomer membrane. The EMI cation diffuses faster than the Tf anion in both the neat state and inside the membrane. We quantitatively evaluate the effects of temperature, IL uptake, and water content. A key factor is the co-existing water content, quantified by in situ1H NMR, which dramatically accelerates the diffusive motion of the IL. When water content, χH2O, drops from 1 to 0.5 water molecules per EMI-Tf, IL diffusion coefficients decrease by 36–60%. Our experiments provide critical feedback for optimizing actuator performance via novel materials, device development, and control of operation conditions.

Study of the incorporation of protic ionic liquids into hydrophilic and hydrophobic rigid-rod elastomeric polymers

A series of polymers was synthesized that contain a rigid aromatic backbone connected through triazine linkages that are cross-linked by flexible diamine-terminated poly(ethylene oxide) oligomers. Polymers were made that contained both hydrophilic sulfonated aromatic and hydrophobic pyridinium triflate backbones. Thermal and mechanical properties of the resulting polymer films were studied, as well as uptake of water and protic ionic liquids. Ionic liquid uptake varied from 41 to 440%, depending upon the nature of the polymer. The ionic liquid-doped films were analyzed for proton conductivity at high temperatures (>150 °C) under non-humidified conditions. Conductivities as high as 5×10 −2 S/cm were observed at 150 °C.