The ionic liquid BmimBr: a dielectric and thermal characterization

Viciosa, María Teresa; Diogo, Hermı́nio P.; Ramos, Joaquim J. Moura

doi:10.1039/c3ra23196h

Cited by 15 publications

(8 citation statements)

References 57 publications

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“…It is believed that large activation entropies and energies reflect cooperative effects among a large number of moving units [19,20], so that those modes are attributed to the main relaxation; it is otherwise to be noted that this deviation from the Starkweather line occurs in the vicinity of Tg. The relaxation map shown in Figure 2 is typical of most of the glass-forming substances (molecular [23], polymeric [24,25] or ionic [14,26]), so that the discrimination of the motional modes of the main-relaxation from those of the secondary relaxations can clearly be made based on the observation of the Starkweather plot. As is well known, an amorphous solid evolves to an equilibrium state through the so-called physical aging process (or structural relaxation), whose rate increases with increasing temperature up to T g .…”

Section: Discrimination By Tsdc Between the Glass Transition And The mentioning

confidence: 99%

Contribution of the technique of thermostimulated currents for the elucidation of the nature of the Johari-Goldstein and other secondary relaxations in the vitreous state

Diogo

Ramos

2014

IEEE Trans. Dielect. Electr. Insul.

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In this work the usefulness of the technique of thermally stimulated depolarization currents (TSDC) to the study of the secondary relaxations in amorphous solids, and particularly of the Johari-Goldstein (JG) relaxation, is emphasized. The features of the JG relaxation are carefully analyzed, and the contribution of this experimental technique for the elucidation of its molecular mechanisms is also stressed.

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Section: Discrimination By Tsdc Between the Glass Transition And The mentioning

confidence: 99%

Contribution of the technique of thermostimulated currents for the elucidation of the nature of the Johari-Goldstein and other secondary relaxations in the vitreous state

Diogo

Ramos

2014

IEEE Trans. Dielect. Electr. Insul.

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“…Thus far, a variety of techniques have been employed to study the relaxation dynamics of ionic liquids at temperatures approaching the glass transition temperature ( T g ), including dielectric spectroscopy, − light scattering, , neutron scattering, , nuclear magnetic resonance (NMR) spectroscopy, , rheology, ,,, Raman spectroscopy, , fluorescence recovery after photobleaching (FRAP), and differential scanning calorimetry. ,− Many other temperature-dependent experiments have also been carried out in the supercooled liquid state, including viscosity measurements − and conductivity measurements. ,− A common observation in glass-forming liquids is that the temperature dependence of viscosity or relaxation time follows the Vogel–Fulcher–Tamman (VFT) − or Williams–Landel–Ferry (WLF) relationship, from which the fragility index m can also be obtained.…”

Section: Introductionmentioning

confidence: 99%

Rheology of Imidazolium-Based Ionic Liquids with Aromatic Functionality

Tao

Simon

2015

J. Phys. Chem. B

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A series of imidazolium-based ionic liquids with cyclic and aromatic groups and a bis[(trifluoromethane)sulfonyl]amide anion were characterized using dynamic and steady shear rheology in a wide temperature range. The cations investigated include 1-(cyclohexylmethyl)-3-methylimidazolium ([CyhmC1im](+)), 1-benzyl-3-methylimidazolium ([BnzC1im](+)), 1,3-dibenzylimidazolium ([(Bnz)2im](+)), and 1-(2-naphthylmethyl)-3-methylimidazolium ([NapmC1im](+)). Rheological properties are reported from terminal flow to the glassy state. All ionic liquids show very similar flow behavior with a glassy modulus approaching 1 GPa. The temperature dependences of the shift factors used for time-temperature superposition and the viscosity both follow the same VFT or WLF relationship, and the dynamic fragility at Tg ranges from 117 to 130 for the aromatic ionic liquids investigated, considerably more fragile, in the Angell sense, than the aliphatic analogs. Additionally, an anomalous aging effect in the dynamic viscosity response (i.e., a maximum observed at intermediate frequencies) was found using a strain-controlled rheometer but not using a stress-controlled rheometer.

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“…The lack of cooperativity observed for the aminobutyric acids is not surprising because of constraints of the crystal lattice and understanding that relaxation at higher temperatures, namely melt/degradation and sublimation, are non-cooperative processes. 23 It is important to note that the T c values observed for both DL-AABA and DL-BABA are below the temperatures of the high temperature thermal events observed using DSC and TGA, whereas in amorphous systems it is generally found to be 5 to 30 1C above the glass transition. 24 The compensation points observed for DL-AABA and DL-BABA could therefore be a point where the cooperative melt, and non-cooperative degradation and sublimation processes actually begin.…”

Section: Discussionmentioning

confidence: 83%

Novel analytical approaches for the study of mobility and relaxation phenomena in positional isomers of GABA

Owusu-Ware

Chowdhry

Leharne

et al. 2013

Phys. Chem. Chem. Phys.

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γ-Aminobutyric acid (GABA), and its positional isomers DL-α-aminobutyric acid (AABA) and DL-β-aminobutyric acid (BABA) have been analysed, in the solid state, using thermally stimulated current (TSC) spectroscopy. Secondary relaxations in these molecules have been detected for the first time. GABA displays two secondary relaxations at 77 ± 2 °C and 114 ± 2 °C, whilst AABA and BABA each display a single secondary relaxation at 109 ± 1 °C and 104 ± 1 °C, respectively. Analysis (decoupling of molecular mobilities) of secondary relaxations using thermal windowing (TW) and relaxation map analysis (RMA) show that the dipole relaxation associated with secondary transitions observed for the aminobutyric acids requires activation energies of 189.9 ± 3.2 kJ mol(-1) (GABA), 142.4 ± 1.4 kJ mol(-1) (AABA) and 195.7 ± 0.8 kJ mol(-1) (BABA). However, the ΔH(≠) values observed were found to exhibit negligible deviations from the zero entropy line. This indicates that the relaxation processes are localised, non-cooperative rotational motions that have a negligible influence on entropy changes of detected molecular mobilities. Furthermore, RMA analysis revealed that AABA and BABA display compensation behaviour i.e., entropy and enthalpy are linearly related to each other, whereas GABA did not demonstrate such behaviour. The coordinates of the compensation point (compensation temperature (Tc) and the compensation relaxation time (τc)) were found to be 214 ± 6 °C and 0.051 ± 0.024 s, respectively for AABA and 153 ± 3 °C and 0.025 ± 0.011 s for BABA. For the molecules investigated the compensation points coincide with the starting temperature of the higher temperature thermal events i.e. sublimation, melt/decomposition, and indicate a correlation between secondary relaxation processes and the main thermal transitions, found via TGA and DSC studies.

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The ionic liquid BmimBr: a dielectric and thermal characterization

Cited by 15 publications

References 57 publications

Contribution of the technique of thermostimulated currents for the elucidation of the nature of the Johari-Goldstein and other secondary relaxations in the vitreous state

Contribution of the technique of thermostimulated currents for the elucidation of the nature of the Johari-Goldstein and other secondary relaxations in the vitreous state

Rheology of Imidazolium-Based Ionic Liquids with Aromatic Functionality

Novel analytical approaches for the study of mobility and relaxation phenomena in positional isomers of GABA

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