Dielectric relaxations of molten acetamide: dependence on the model interaction potentials and the effects of system size

Maji, Dhrubajyoti; Indra, Sandipa; Biswas, Ranjit

doi:10.1007/s12039-021-01973-8

Cited by 7 publications

(6 citation statements)

References 59 publications

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“…to overestimate the experimental DR times by a factor of ~2. 39 The simulated slower than experimental relaxation times fails to correctly describe the viscosity coupling of the diffusive dynamics, and as a result, the simulated DR activation energies show an anion dependence reverse of that found in measurements. An additional support to this view comes from a previous simulation study 105 which reported a much weaker decoupling between the centre-ofmass diffusion and viscosity than reported in experiments.…”

Section: Frequency-dependent Dielctric Function: Connection To Experi...mentioning

confidence: 86%

“…OPLS (optimized potentials for liquid simulations) type model force field were used 81 . Since the functional forms and notations associated with different pieces of the OPLS model potential were discussed earlier 39 , these are provided in the Appendix A1 (supplementary material). Interaction parameters developed 82 for correctly reproducing the experimental 83 𝜀 𝑠 of neat molten acetamide were employed to represent the acetamide molecules.…”

Section: Simulation Details and Validationmentioning

confidence: 99%

“…This forms the basis of the present work where we have used molecular dynamics simulations coupled with classical, coarse-grained model interaction potentials to monitor the time dependent fluctuations of the collective dipole moment of these ionic DESs. Our previous simulation study 39 of DR in neat molten acetamide employing the same model interaction potential acts as a supporting work to understand, at least, qualitatively the effects of ion on the rotational, translational and ro-translational contributions to the complex dielectric relaxation spectra recorded in experiments. In this context we would like to mention that DR measurements of conducting media such as these ionic DESs in the low frequency wing is severely limited by one-over-frequency (1 𝜔 ⁄ ) divergence.…”

Section: Introductionmentioning

confidence: 99%

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Dielectric relaxation and dielectric decrement in ionic acetamide deep eutectic solvents: Spectral decomposition and comparison with experiments

Maji

Biswas

2023

Preprint

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Frequency dependent dielectric relaxation in the three deep eutectic solvents (DESs), (acetamide+LiClO4/NO3/Br), was investigated in the temperature range, 329T/K358, via molecular dynamics (MD) simulations. Subsequently, decomposition of the real and the imaginary components of the simulated dielectric spectra was carried out to separate the rotational (dipole-dipole), translational (ion-ion) and ro-translational (dipole-ion) contributions. The dipolar contribution, as expected, was found to dominate all the frequency dependent dielectric spectra over the entire frequency regime, while the other two components together made tiny contributions only. The translational (ion-ion) and the cross ro-translational contributions appeared in the THz regime in contrast to the viscosity dependent dipolar relaxations that dominated the MHz-GHz frequency window. Our simulations predicted, in agreement with experiments, anion dependent decrement of the static dielectric constant (_s ~ 20 - 30) for acetamide (_s ~66) in these ionic DESs. Simulated dipole-correlations (Kirkwood g factor) indicated significant orientational frustrations. The frustrated orientational structure was found to be associated with the anion dependent damage of the acetamide H-bond network. Single dipole reorientation time distributions suggested slowed down acetamide rotations but did not indicate presence of any rotationally frozen molecules. The dielectric decrement is, therefore, largely static in origin. This provides a new insight into the ion dependence of the dielectric behaviour of these ionic DESs. A good agreement between the simulated and the experimental timescales was also noticed.

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Section: Frequency-dependent Dielctric Function: Connection To Experi...mentioning

confidence: 86%

Section: Simulation Details and Validationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Dielectric relaxation and dielectric decrement in ionic acetamide deep eutectic solvents: Spectral decomposition and comparison with experiments

Maji

Biswas

2023

Preprint

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“…The simulated frequency-dependent dielectric function, ε(ω) can be obtained from the normalized total dipole moment autocorrelation function, ϕ( t ), which is given by , ϕ false( t false) = ⟨ M false( 0 false) · M false( t false) ⟩ ⟨ false| M false( 0 false) false| 2 ⟩ where total dipole moment, M ( t ) = ∑ i μ i ( t ), where μ i is the dipole moment of the individual dipolar molecules.…”

Section: Theory and Computational Detailsmentioning

confidence: 99%

Temperature-Dependent Dielectric Relaxation Measurements of (Betaine + Urea + Water) Deep Eutectic Solvent in Hz-GHz Frequency Window: Microscopic Insights into Constituent Contributions and Relaxation Mechanisms

Mondal,

Maji,

Mitra

et al. 2024

J. Phys. Chem. B

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A combined experimental and simulation study of dielectric relaxation (DR) of a deep eutectic solvent (DES) composed of betaine, urea, and water with the composition [Betaine:Urea:Water = 11.7:12:1 (weight ratio) and 9:18:5 (molar ratio)] was performed to explore and understand the interaction and dynamics of this system. Temperature-dependent (303 ≤ T/K ≤ 343) measurements were performed over 9 decades of frequency, combining three different measurement setups. Measured DR, comprising four distinct steps with relaxation times spreading over a few picoseconds to several nanoseconds, was found to agree well with simulations. The simulated total DR spectra, upon dissection into three self (intraspecies) and three cross (interspecies) interaction contributions, revealed that the betaine− betaine self-term dominated (∼65%) the relaxation, while the urea−urea and water−water interactions contributed only ∼7% and ∼1%, respectively. The cross-terms (betaine−urea, betaine−water, and urea−water) together accounted for <30% of the total DR. The slowest DR component with a time constant of ∼1−10 ns derived dominant contribution from betaine−betaine interactions, where betaine−water and urea−water interactions also contributed. The subnanosecond (0.1−0.6 ns) time scale originated from all interactions except betaine−water interaction. An extensive interaction of water with betaine and urea severely reduced the average number of water−water H-bonds (∼0.7) and heavily decreased the static dielectric constant of water in this DES (ε s ∼ 2). Furthermore, simulated first rank collective single particle reorientational relaxations (C 1 (t)) and the structural H-bond fluctuation dynamics (C HB (t)) exhibited multiexponential kinetics with time scales that corresponded well with those found both in the simulated and measured DR.

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“…27 This is because this force field describes well the experimental densities 15 (deviation being ≤3%) and reproduces the experimental static dielectric constant 12 and other liquid properties for molten acetamide, 27 although dielectric relaxation time constants and translational diffusion constants were found to be considerably slower than those predicted by its OPLS-AA counterpart. 42,43 A comparison between the simulated (by using the OPLS-UA model potential) and experimental densities is shown in Figure 1 for these two DESs at different temperatures.…”

Section: Validation Of the Simulation Force Fieldmentioning

confidence: 99%

Difference in “Supercooling” Affinity between (Acetamide + Na/KSCN) Deep Eutectics: Reflections in the Simulated Anomalous Motions of the Constituents and Solution Microheterogeneity Features

et al. 2022

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Deep depression of freezing points of ionic amide deep eutectic solvents (DESs) is known to exhibit a significant dependence on the identity of ions present in those systems and the nature of the functional group attached to the host amide. This deep depression of the freezing point is sometimes termed as “supercooling”. For (acetamide + electrolyte) DESs, experiments have revealed signatures of ion-dependent spatiotemporal heterogeneity features. The focus of this work is to provide microscopic explanations of these experimentally observed macroscopic system properties in terms of particle jumps and insights about the origin of the cation dependence. For this purpose, extensive molecular dynamics simulations have been performed employing (acetamide + Na/KSCN) deep eutectics as representative ionic systems at 303, 318, 333, and 348 K. The individual translational motions of acetamide and the ions are followed, and their connections to solution heterogeneity are explored. The center-of-mass motion for Na+ has been found to be more anomalous than that for K+. This difference corroborates well with experimental reports on heterogeneous relaxations in these systems. Simulated viscosity coefficients and dynamic heterogeneity features also reflect this difference. Moreover, simulated reorientational relaxations of acetamide molecules in these ionic DESs suggest that a Na+-containing DES is more heterogeneous than the corresponding K+-containing system. Estimated void and neck distributions for acetamide molecules differ as the alkali metal ions differ. In brief, this study provides a detailed microscopic view of the cation dependence of the microheterogeneous relaxation dynamics of these DESs reported repeatedly by different experiments.

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Dielectric relaxations of molten acetamide: dependence on the model interaction potentials and the effects of system size

Cited by 7 publications

References 59 publications

Dielectric relaxation and dielectric decrement in ionic acetamide deep eutectic solvents: Spectral decomposition and comparison with experiments

Dielectric relaxation and dielectric decrement in ionic acetamide deep eutectic solvents: Spectral decomposition and comparison with experiments

Temperature-Dependent Dielectric Relaxation Measurements of (Betaine + Urea + Water) Deep Eutectic Solvent in Hz-GHz Frequency Window: Microscopic Insights into Constituent Contributions and Relaxation Mechanisms

Difference in “Supercooling” Affinity between (Acetamide + Na/KSCN) Deep Eutectics: Reflections in the Simulated Anomalous Motions of the Constituents and Solution Microheterogeneity Features

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