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

06 March 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


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.


Dielectric Relaxation Spectroscopy
Computer Simulations
Deep Eutectic Solvents

Supplementary materials

Supporting Information for the article entitled, "Dielectric relaxation and dielectric decrement in ionic acetamide deep eutectic solvents: Spectral decomposition and comparison with experiments"
The supplementary material contains Number of constituent particles in the three DESs, functional form of the OPLS potential model, atomic representations of DES molecules, comparison between temperature-dependent simulated and measured densities of DESs, brief description of calculating dielectric spectra from simulation trajectory, fit parameters for rotational, translational and ro-translational correlation functions at different temperatures, temperature-dependent multi-exponential fit parameters for the simulated C_HB (t), C_1 (t), and DR timescales, Comparison between static dielectric constant and dielectric relaxation times obtained from simulation and experiments for three the DESs, analysis protocol to calculate number of hydrogen bonds.


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