Pierre-Henri Aubert

Ionic liquids and γ-butyrolactone mixtures as electrolytes for supercapacitors operating over extended temperature ranges

Physicochemical and electrochemical properties of three different ionic liquids (1-propyl-1 methylpyrrolidinium bis(fluorosulfonyl)imide – Pyr13FSI, 1-butyl-1-methylpyrrolidinium bis(trifluoro methanesulfonyl)imide – Pyr14TFSI and 1-ethyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide – EMITFSI) were investigated and compared with binary mixtures of those ionic liquids with γ-butyrolactone (GBL). It was found that the highest conductivity for each mixture was obtained for a concentration close to 50 wt%. Then thermal and transport properties for the three neat ionic liquids and the three mixtures with GBL at 50 wt% were evaluated from −50 °C to 100 °C. The addition of GBL enhances the conductivity and fluidity of the mixtures, especially at low temperature. For instance, at −50 °C the ionic conductivity for EMITFSI/GBL is still as high as 1.9 mS cm−1 and its viscosity is 70 mPa s. Another advantage of the solvent addition is that it suppresses the melting transition and allows applications down to −50 °C. A drawback is the slight reduction of the electrochemical stability window of the electrolyte.

Conducting polymer nanofibers with controlled diameters synthesized in hexagonal mesophases

Oil-swollen hexagonal mesophases resulting from the surfactant mediated self-assembly of a quaternary mixture of water, surfactant, co-surfactant, and oil, are versatile templates to synthesize anisotropic nanomaterials. Poly(diphenylbutadyine) (PDPB) polymer nanofibrous network structures were produced in the oil tubes of the mesophases by photo-induced radical polymerization using a chemical initiator or by gamma irradiation. The diameter of the nanofibers can be varied from 5 to 25 nm in a controlled fashion, and is directly determined by the diameter of the oil tube of the doped mesophases, proving thus a direct templating effect of the mesophase. The nanoIR technique allows chemical characterization and identification of the polymer nanostructures simultaneously with morphological characterization. Cyclic voltammetry has been used as an effective approach to evaluate both the energy level of the highest occupied molecular orbital (HOMO) as well as the energy of the lowest unoccupied molecular orbital (LUMO) and the band gap of the PDPB. The conductivity of the PDPB nanostructures obtained by gamma irradiation was estimated to be 10−1 S cm−1, which is higher than the conductivity of PDPB nanostructures previously reported in the literature. The soft template approach allows size tunable synthesis of anisotropic polymer structures with morphological homogeneity at the nanoscale with high conductivity, thus it appears to be an attractive opportunity for electronic device applications.

Understanding the colorimetric properties of quinoxaline-based pi-conjugated copolymers by tuning their acceptor strength: a joint theoretical and experimental approach

A series of five new π-conjugated donor–acceptor–donor (DADn) copolymers are presented, combining a common donating unit (substituted propylenedioxythiophene, ProDOT-(OEtHx)) with five diphenyl-quinoxaline based acceptor units bearing substituents of increasing acceptor strength (OMe < H < F < COOMe < CN). The DADn copolymers, namely P3-X (X = OMe, H, F, COOMe, CN), have been studied in solid state by cyclic voltammetry to investigate their electronic properties during n- and p-doping processes and to determine their electrochemical band gap. UV-Vis spectroscopy reveals a dual-band absorption system in which both high energy and low energy band (HEB and LEB) positions and intensities are governed by the acceptor strength. Density functional theory (DFT) computations were performed on D–A–D trimer model compounds in order to understand the experimental results. A colorimetric study in the CIELAB color space revealed that the modulation of the acceptor strength with σ- or π-electron withdrawing/donating groups leads to shades of blue to green upon increasing the acceptor strength. The polymers can also switch to a grey color upon p-doping. Finally, a detailed discussion on color–structure relationship provides valuable insights on molecular design principles to render cyan and green colors.

Conducting IPNs and Ionic Liquids: Applications to Electroactive Polymer Devices

The synthesis of interpenetrating polymer networks (IPNs) is proposed as an alternative to polyether-based (co)polymers or networks for the design of solid polymer electrolytes (SPEs). IPNs were prepared from an elastomer bringing the mechanical properties and poly(ethylene oxide). These IPNs, swollen by N-ethylmethylimidazolium bis(trifluoromethanesulfonyl)-imide (EMITFSI), possess an ionic conductivity close to 10−3 S cm−1 at 30 °C. In order to form conducting IPNs, chemical polymerization of 3,4-ethylenedioxythiophene (EDOT) has been carried out within the SPE IPN. A pseudo-trilayer configuration has been obtained with the SPE IPN sandwiched between two interpenetrated PEDOT electrodes. Controlling the PEDOT content from 0.3 to 24 wt% in the material, electrochromic, electroreflective, or electromechanical devices is obtained.