Solid-Contact Ion-Selective and Reference Electrodes Covalently Attached to Functionalized Poly(ethylene terephthalate).

Numerous ion-selective and reference electrodes have been developed over the years. Following the need for point-of-care and wearable sensors, designs have transitioned recently from bulky devices with an aqueous inner filling solution to planarizable solid-contact electrodes. However, unless the polymeric sensing and reference membranes are held in place mechanically, delamination of these membranes from the underlying solid to which they adhere physically limits sensor lifetime. Even minor external mechanical stress or thermal expansion can result in membrane delamination and, thereby, device failure. To address this problem, we designed a sensing platform based on poly(ethylene terephthalate) substrates to which polyacrylate-based sensing and polymethacrylate-based reference membranes are attached covalently. Ion-selective membranes with covalently attached or freely dissolved ionophore- and ionic-liquid-doped reference membranes can be directly photopolymerized onto surface-functionalized poly(ethylene terephthalate), resulting in the formation of covalent bonds between the underlying substrate and the attached membranes. H+- and K+-selective electrodes thus prepared exhibit highly selective responses with the theoretically expected (Nernstian) response slope, and reference electrodes provide sample-independent reference potentials over a wide range of electrolyte concentrations. Even repeated mechanical stress does not result in the delamination of the sensing and reference membranes, leading to electrodes with much improved long-term performance. As demonstrated for poly(ethylene-co-cyclohexane-1,4-dimethanol terephthalate) (PETG), this approach may be expanded to a wide range of other polyester, polyamide, and polyurethane platform materials. Covalent attachment of sensing and reference membranes to an inert plastic platform material is a very promising approach to a problem that has plagued the field of ion-selective electrodes and field effect transistors for over 30 years.

The Use of Succinonitrile as an Electrolyte Additive for Composite-Fiber Membranes in Lithium-Ion Batteries.

In the present work, the effect of temperature and additives on the ionic conductivity of mixed organic/ionic liquid electrolytes (MOILEs) was investigated by conducting galvanostatic charge/discharge and ionic conductivity experiments. The mixed electrolyte is based on the ionic liquid (IL) (EMI/TFSI/LiTFSI) and organic solvents EC/DMC (1:1 v/v). The effect of electrolyte type on the electrochemical performance of a LiCoO2 cathode and a SnO2/C composite anode in lithium anode (or cathode) half-cells was also investigated. The results demonstrated that the addition of 5 wt.% succinonitrile (SN) resulted in enhanced ionic conductivity of a 60% EMI-TFSI 40% EC/DMC MOILE from ~14 mS·cm-1 to ~26 mS·cm-1 at room temperature. Additionally, at a temperature of 100 °C, an increase in ionic conductivity from ~38 to ~69 mS·cm-1 was observed for the MOILE with 5 wt% SN. The improvement in the ionic conductivity is attributed to the high polarity of SN and its ability to dissolve various types of salts such as LiTFSI. The galvanostatic charge/discharge results showed that the LiCoO2 cathode with the MOILE (without SN) exhibited a 39% specific capacity loss at the 50th cycle while the LiCoO2 cathode in the MOILE with 5 wt.% SN showed a decrease in specific capacity of only 14%. The addition of 5 wt.% SN to the MOILE with a SnO2/C composite-fiber anode resulted in improved cycling performance and rate capability of the SnO2/C composite-membrane anode in lithium anode half-cells. Based on the results reported in this work, a new avenue and promising outcome for the future use of MOILEs with SN in lithium-ion batteries (LIBs) can be opened.

Preparation, Characterization, and Formulation Development of Drug-Drug Protic Ionic Liquids of Diphenhydramine with Ibuprofen and Naproxen.

Diphenhydramine (DPH) has been used with ibuprofen (IBU) or naproxen (NAP) in combined therapies to provide better clinical efficacy as an analgesic and sleep aid. We discovered that DPH can form protic ionic liquids (PILs) with IBU and NAP, which opens the opportunity for a new delivery mode of these combination drugs. [DPH][IBU] and [DPH][NAP] PILs exhibit low ionicity, as confirmed by Fourier transform infrared and 1H NMR spectroscopy, and accompanied by low diffusivity, high viscosity, and poor ionic conductivity. Evaluation of pharmaceutical properties of the two PILs showed that these PILs, despite high solubility and good wettability, exhibited low dissolution rates, owing to the poor dispersion of the PIL drops and the resultant small surface area during dissolution. However, when loaded into a mesoporous carrier, the PIL-carrier composites exhibited improved dissolution rates along with excellent flow properties and easy handling. Oral capsules of both PILs were developed using such composites. Such capsule products exhibited acceptable drug release and bioavailability as demonstrated by a predictive artificial stomach-duodenum dissolution test.

Self-Supporting, Hydrophobic, Ionic Liquid-Based Reference Electrodes Prepared by Polymerization-Induced Microphase Separation.

Interfaces of ionic liquids and aqueous solutions exhibit stable electrical potentials over a wide range of aqueous electrolyte concentrations. This makes ionic liquids suitable as bridge materials that separate in electroanalytical measurements the reference electrode from samples with low and/or unknown ionic strengths. However, methods for the preparation of ionic liquid-based reference electrodes have not been explored widely. We have designed a convenient and reliable synthesis of ionic liquid-based reference electrodes by polymerization-induced microphase separation. This technique allows for a facile, single-pot synthesis of ready-to-use reference electrodes that incorporate ion conducting nanochannels filled with either 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide or 1-dodecyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imide as ionic liquid, supported by a mechanically robust cross-linked polystyrene phase. This synthesis procedure allows for the straightforward design of various reference electrode geometries. These reference electrodes exhibit a low resistance as well as good reference potential stability and reproducibility when immersed into aqueous solutions varying from deionized, purified water to 100 mM KCl, while requiring no correction for liquid junction potentials.

Robust Polymer Electrolyte Membranes with High Ambient-Temperature Lithium-Ion Conductivity via Polymerization-Induced Microphase Separation.

Mechanically robust polymer electrolyte membranes (PEMs) exhibiting high ionic conductivity at ambient temperature are a prerequisite for next-generation electrochemical devices. We utilized a polymerization-induced microphase separation (PIMS) strategy to prepare nanostructured materials comprising continuous conducting nanochannels intertwined with a mechanically and thermally robust cross-linked polymeric framework. Addition of succinonitrile (SN) rendered the poly(ethylene oxide)/lithium (Li) salt conducting domains completely amorphous, resulting in outstanding conductivities (∼0.35 mS/cm) at 30 °C. Concurrently, a densely cross-linked polystyrene framework provided mechanical robustness (modulus E' ≈ 0.3 GPa at 30 °C) to the hybrid material. This work highlights a facile, single-pot strategy involving a homogeneous liquid reaction precursor that yields a high-performance ion-conducting membrane attractive for lithium-battery applications.

Anhydrous Proton Conducting Polymer Electrolyte Membranes via Polymerization-Induced Microphase Separation.

Solid-state polymer electrolyte membranes (PEMs) exhibiting high ionic conductivity coupled with mechanical robustness and high thermal stability are vital for the design of next-generation lithium-ion batteries and high-temperature fuel cells. We present the in situ preparation of nanostructured PEMs incorporating a protic ionic liquid (IL) into one of the domains of a microphase-separated block copolymer created via polymerization-induced microphase separation. This facile, one-pot synthetic strategy transforms a homogeneous liquid precursor consisting of a poly(ethylene oxide) (PEO) macro-chain-transfer agent, styrene and divinylbenzene monomers, and protic IL into a robust and transparent monolith. The resulting PEMs exhibit a bicontinuous morphology comprising PEO/protic IL conducting pathways and highly cross-linked polystyrene (PS) domains. The cross-linked PS mechanical scaffold imparts thermal and mechanical stability to the PEMs, with an elastic modulus approaching 10 MPa at 180 °C, without sacrificing the ionic conductivity of the system. Crucially, the long-range continuity of the PEO/protic IL conducting nanochannels results in an outstanding ionic conductivity of 14 mS/cm at 180 °C. We posit that proton conduction in the protic IL occurs via the vehicular mechanism and the PEMs exhibit an average proton transference number of 0.7. This approach is very promising for the development of high-temperature, robust PEMs with excellent proton conductivities.