Temperature and Pressure Induced Structural Changes of Cobalt (II) in a Phosphonium Based Ionic Liquid

The temperature- and pressure-induced paramagnetic switching of cobalt(II) complex in a binary mixture of phosphoniumbased ionic liquid [P6,6,6,14]SCN and [Co(NCS)2] is reported. This arises from a structural change in the coordination of the cobalt(II) center from tetrahedral [Co(NCS)4]2− to octahedral [Co(NCS)6]4− when mobile thiocyanate ions are added. These properties are reflected in the abrupt change of the conductivity behavior of the magnetic ionic liquid. Therefore, as demonstrated herein, the reversible switching in coordination of cobalt from tetrahedral to octahedral can be easily monitored at ambient as well as elevated pressure by tracking the dc-conductivity changes

Communication: Inflection in the pressure dependent conductivity of the protic ionic liquid C8HIM NTf2

International audienceTemperature and pressure dependent broadband dielectric measurements were performed on the protic ionic liquid C8HIM NTf2 over a frequency range from 0.1 Hz to 1 MHz. The temperature dependence of the inverse dc-conductivity exhibits the super-Arrhenius like behavior typical for glass forming materials. However, in the pressure dependence both slower and faster than exponential developments occur, resulting in an inflection in the corresponding curves. The experimental data was successfully fitted with a model incorporating both features. While similar transitions have been observed in the pressure dependent viscosity or structural relaxation times, this is the first time such a behavior is reported in the conductivity

Can the scaling behavior of electric conductivity be used to probe the self-organizational changes in solution with respect to the ionic liquid structure? The case of [C8MIM][NTf2]

Scaling exponent as a key parameter to probe self-organization changes in solution with respect to the IL structure.</p

Revealing Fast Proton Transport in Condensed Matter by Means of Density Scaling Concept

Herein, we investigate the charge transport and structural dynamics in the supercooled and glassy state of protic ionic material with an efficient interionic Grotthuss mechanism. We found that superprotonic properties of studied acebutolol hydrochloride (ACB-HCl) depend on thermodynamic conditions with the most favorable regions being close to the glass-transition temperature (Tg) and glass-transition pressure (Pg). To quantify the contribution of fast proton hopping to overall charge transport over a broad T–P space, we employed the density scaling concept, one of the most important experimental findings in the field of condensed matter physics. We found that isothermal and isobaric dc-conductivity (σdc) and dynamic light scattering (τα) data of ACB-HCl plotted as a function of (TVγ)−1 satisfy the thermodynamic scaling criterion with the ratio γσ/γα appearing as a new measure of fast charge transport in protic ionic glass-formers in the T–P plane. Such a universal factor becomes an alternative to the well-known Walden rule being limited to ambient pressure conditions

Synthesis, characterization and dielectric relaxation study of hyperbranched polymers with different molecular architecture

Hyperbranched polymers are macromolecular systems of high branching density. They play a key role in the forefront of macromolecular synthesis for having features different from those of non-hyperbranched polymers and unique properties that make them amenable for use in a variety of applications. This paper presents the results from the synthesis of hyperbranched polymers of different molecular architecture, i.e., spherical and cylindrical. Also characterization of their thermal and dynamic properties is provided. Atom transfer radical polymerization from star and linear pre-former macroinitiators produced hyperbranched systems based on methyl methacrylate and lauryl methacrylate. Thermal characterizations by TGA and DSC allowed different types of interactions and degradation mechanisms as a function of the determined polymer architecture. NMR studies revealed the effect of molecular architecture on monomers tacticity along the molecular brushes. Spherical architecture yielded a higher isotactic percentage than cylindrical architecture did, thus indicating a specific stereochemistry as a function of the macro-initiator morphology. Broadband dielectric spectroscopy, one of the most powerful techniques to study the dynamics of molecular systems revealed not only different patterns of behavior of hyperbranched polymers of different architectures but also results in agreement with NMR on stereochemistry as a function of molecular architecture.Fil: Giussi, Juan Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Azzaroni, Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Hensel-Bielowka, Stella. University of Silesia; PoloniaFil: Wojnarowska, Zaneta. University of Silesia; Polonia. Silesian Center for Education and Interdisciplinary Research; PoloniaFil: Knapik, Justyna. University of Silesia; Polonia. Silesian Center for Education and Interdisciplinary Research; PoloniaFil: Paluch, Marian. University of Silesia; Polonia. Silesian Center for Education and Interdisciplinary Research; Poloni

Comparative study of effect of alkyl chain length on thermophysical characteristics of five N-alkylpyridinium bis(trifluoromethylsulfonyl)imides with selected imidazolium-based ionic liquids

International audienceThe series of N-alkylpyridiniumbis(trifluoromethylsulfonyl)imide, [Cnpy][NTf2],where n=2, 3, 4, 6, and 8 havebeen synthesized and the effect of alkyl chain length in cation on their thermophysical properties have been studiedand compared with those observed in analogous imidazolium-based ILs. To drive this comparison, the speedof sound, density, isobaric heat capacity, electric conductivity, TGA for all [Cnpy][NTf2], aswell as, refractive indexof [Cnpy][NTf2] (n = 3, 6) and surface tension of [Cnpy][NTf2] (n = 2, 4, 6, 8) were determined as a function oftemperature at atmospheric pressure. From these experimental data, the isentropic compressibility, isobaricthermal expansion, isothermal compressibility, isochoric heat capacity, internal pressure, as well as, the surfaceentropy and surface enthalpy were calculated. The electric conductivity together with the literature viscositydata are used to obtain the Walden plot for the investigated ionic liquids. The minimum of the speed of sounddependence on the alkyl chain length in the cation is observed for [C6py][NTf2]. The isentropic compressibilityand the isothermal compressibility of [Cnpy][NTf2] increase with increasing alkyl chain length in the cation andthe slope of this dependence is changed around n = 6. These effects were more pronounced than that forimidazolium-based ionic liquids with [NTf2]− anion. Finally, COSMOthermX software was used to further evaluateits predictive capability by comparing calculated density and isobaric heat capacity as a function of the ILstructure and temperature with experimental data for the [Cnpy][NTf2] (n = 2, 3, 4, 6, 8) series. This analysisshows a very good agreement in the case of the Cp with an average absolute relative deviation close to 1.4%while a deviation close to 0.72% is observed in the case of the density of the [Cnpy][NTf2]

Pressure-induced liquid-liquid transition in a family of ionic materials

Liquid−liquid transition (LLT) between two disordered phases of single-component material remains one of the most intriguing physical phenomena. Here, we report a first-order LLT in a series of ionic liquids containing trihexyl(tetradecyl)phosphonium cation [P666,14]+ and anions of different sizes and shapes, providing an insight into the structure-property relationships governing LLT. In addition to calorimetric proof of LLT, we report that ion dynamics exhibit anomalous behavior during the LLT, i.e., the conductivity relaxation times (τσ) are dramatically elongated, and their distribution becomes broader. This peculiar behavior is induced by isobaric cooling and isothermal compression, with the τσ(TLL,PLL) constant for a given system. The latter observation proves that LLT, in analogy to liquid-glass transition, has an isochronal character. Finally, the magnitude of discontinuity in a specific volume at LLT was estimated using the Clausius-Clapeyron equation