Dielectric Relaxation and Solvation Dynamics in a Room-Temperature Ionic Liquid: Temperature Dependence

Abstract

Dielectric relaxation, related polarization and conductivity, and solvation dynamics of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMI(+)PF6(-)) are studied via molecular dynamics computer simulations in the temperature range 300 K ≤ T ≤ 500 K. Two main bands of its dielectric loss spectrum show differing temperature behaviors. As T increases, the absorption band in the microwave region shifts to higher frequencies rapidly, whereas the location of the bimodal far-IR band remains nearly unchanged. Their respective intensities tend to decrease and increase. The static dielectric constant of BMI(+)PF6(-) is found to decrease weakly with T. The ultrafast inertial component of solvation dynamics remains largely unchanged, while their dissipative relaxation component becomes faster. Roles played by ion reorientations and translations in governing dynamic and static dielectric properties of the ionic liquid are examined. A brief comparison with available experimental results is also made.

Solvation dynamics: improved reproduction of the time-dependent Stokes shift with polarizable empirical force field chromophore models

“…The investigation of solvent properties via calculation or measurement of the time-dependent Stokes shift (TDSS) has been of high interest during the last decades. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] The TDSS probes the timescale of solvent rearrangement by excitation of a dissolved chromophore, which causes the solvent to reorganize and the wavelength of the emitted fluorescence light of the chromophore to change. Upon excitation, both the dipole moment and the polarizability of the chromophore change, so that both the electrostatic and dispersion interactions change.…”

Dynamics of electrical double layer formation in room-temperature ionic liquids under constant-current charging conditions

“…The structure and capacitance of EDLs in RTILs under equilibrium conditions have been extensively studied both using experimental techniques, [3][4][5][6][7][8][9] and theoretically by analytical modeling, [10][11][12] atomistic simulations, [13][14][15][16][17][18][19][20] and classical density functional theory calculations [21]. Thanks to these works, many interesting phenomena such as over-screening, lattice saturation, alternating layering of ions near electrode surface and the diverse shape of capacitancevoltage curves are now reasonably well understood.…”

Nonpolar solvation dynamics for a nonpolar solute in room temperature ionic liquid: a nonequilibrium molecular dynamics simulation study

“…61 The rationale of using this force field, apart from the fact that the use of this force field results into much less computational cost compared to that of the polarizable model, is its proven predictability of the measured solvation and dielectric relaxation behavior of a dipolar solute dissolved in RTILs. 33,34,38,39 An alternate model reducing the charges of the RTIL ions to enhance the mobility also does exist. This model is based on the understanding that due to the induced polarization between the ions of RTIL the columbic charges of the ions are less than whole numbers (±1).…”

“…[10][11][12][13][14][15][16][17][18][19][20][21][22][23] While it is somewhat settled that the origin of the slower relaxation is usually due to the slower rotation of the dipolar cations and/or the translation of the ions, the origin of the ultrafast time constant is still debated. [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] Multiple modes of molecular movements can be responsible for this ultrafast relaxation, including the hydrogen-bond (H-bond) libration, [25][26][27][28][29][30][31] faster rotation of the dipolar cation, [24][25][26][27][28][29] fast translation of small constitute anion, 10,[37]<...>…”