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A group of new zwitterion based ionic liquid crystals (ILCs) have been synthesized. Depending on the counter anion (mesylate or hydrogen sulfate) the phase behavior of the resulting ILCs is quite different. Mesylate based ILCs show complex phase behavior with multiple phases depending on the alkyl chain length. In contrast, hydrogen sulfate based systems always exhibit Colr phases irrespective of the alkyl chain length. The latter show much larger ILC mesophase windows and are thermally stable up to ca. 200 °C. All ILCs show reasonable ionic conductivities of up to 10−4 S cm−1 at elevated temperatures, making these ILCs candidates for intermediate temperature ionic conductors. [ABSTRACT FROM AUTHOR]

The present study was designed to investigate the physical stability of three organic materials with similar chemical structures. The examined compounds revealed completely different crystallization tendencies in their supercooled liquid states and were classified into three distinct classes based on their tendency to crystallize. (S)-4-Benzyl-2-oxazolidinone easily crystallizes during cooling from the melt; (S)-4-Benzylthiazolidine-2-thione does not crystallize during cooling from the melt, but crystallizes easily during subsequent reheating above Tg; and (S)-4-Benzyloxazolidine-2-thione does not crystallize either during cooling from the melt or during reheating. Such different tendencies to crystallize are observed despite the very similar chemical structures of the compounds, which only differ in oxide or sulfur atoms in one of their rings. We also studied the isothermal crystallization kinetics of the materials that were shown to transform into a crystalline state. Molecular dynamics and thermal properties were thoroughly investigated using broadband dielectric spectroscopy, as well as conventional and temperature-modulated differential scanning calorimetry in the wide temperature range. It was found that all three glass formers have the same dynamic fragility (m = 93), calculated directly from dielectric structural relaxation times. This result verifies that dynamic fragility is not related to the tendency to crystallize. In addition, thermodynamic fragility predictions were also made using calorimetric data. It was found that the thermodynamic fragility evaluated based on the width of the glass transition, observed in the temperature dependence of heat capacity, correlates best with the tendency to crystallize. [ABSTRACT FROM AUTHOR]

In this paper, we have examined a series of phenyl-substituted primary monohydroxy alcohols (phenyl alcohols, PhAs), from ethanol to hexanol by means of dielectric and Fourier transform infrared (FTIR) spectroscopies supported by the mechanical investigations. The combination of both dielectric and mechanical data allows calculation of the energy barrier, Ea, for dissociation by the Rubinstein approach developed to describe the dynamical properties of self-assembling macromolecules. It was observed that the determined activation energy remains constant, ‖Ea,RM‖ ∼ 12.9–14.2 kJ mol−1, regardless of the molecular weight of the examined material. Surprisingly, the obtained values agree very well with Ea of the dissociation process determined from the FTIR data analysed within the van't Hoff relationship, where Ea,vH ∼ 9.13–13.64 kJ mol−1. Thus, the observed agreement between Ea determined by both applied approaches clearly implies that in the case of the examined series of PhAs, the dielectric Debye-like process is governed by the association–dissociation phenomenon as proposed by the transient chain model. [ABSTRACT FROM AUTHOR]

A detailed investigation on the molecular dynamics of ionic deep eutectic solvents (acetamide +lithium nitrate/sodium thiocyanate) is reported. The study was carried out employing dielectric relaxation spectroscopy covering seven decades in frequency (10-1-106 Hz) and in a wide temperature range from 373 K down to 173 K, accessing the dynamic observables both in liquid and glassy state. The dielectric response of the ionic system has been presented in the dynamic window of modulus formalism to understand the conductivity relaxation and its possible connection to the origin of localized motion. Two secondary relaxation processes appear below glass transition temperature. Our findings provide suitable interpretation on the nature of secondary Johari-Goldstein process describing the ion translation and orientation of dipoles in a combined approach using Ngai's coupling model. A nearly constant loss feature is witnessed at shorter times/lower temperatures. We also discuss the ac conductivity scaling behavior using Summerfield approach and random free energy barrier model which establish the time-temperature superposition principle. These experimental observations have fundamental importance on theoretical elucidation of the conductivity relaxation and glass transition phenomena in molten ionic conductors. [ABSTRACT FROM AUTHOR]

Temperature 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. [ABSTRACT FROM AUTHOR]

Temperature 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. [ABSTRACT FROM AUTHOR]