Hindered molecular reorientation of lithium ion doped succinonitrile in the terahertz range
The THz range permittivity of succinonitrile exhibits Debye-like behavior in its plastic-crystal phase, with a characteristic Cole-Cole relaxation time of 65ps ±17ps which increases considerably in the presence of ionic dopants.
Dielectric relaxation spectroscopy for evaluation of the influence of solvent dynamics on ion transport in succinonitrile-salt plastic crystalline electrolytes.
Influence of succinonitrile (SN) dynamics on ion transport in SN-lithium perchlorate (LiClO(4)) electrolytes is discussed here via dielectric relaxation spectroscopy. Dielectric relaxation spectroscopy (∼2×10(-3) Hz to 3 MHz) of SN and SN-LiClO(4) was studied as a function of salt content (up to 7 mol % or 1 M) and temperature (-20 to +60 °C). Analyses of real and imaginary parts of permittivity convincingly reveal the influence of trans-gauche isomerism and solvent-salt association (solvation) effects on ion transport. The relaxation processes are highly dependent on the salt concentration and temperature. While pristine SN display only intrinsic dynamics (i.e., trans-gauche isomerism) which enhances with an increase in temperature, SN-LiClO(4) electrolytes especially at high salt concentrations (∼0.04-1 M) show salt-induced relaxation processes. In the concentrated electrolytes, the intrinsic dynamics was observed to be a function of salt content, becoming faster with an increase in salt concentration. Deconvolution of the imaginary part of the permittivity spectra using Havriliak-Negami (HN) function show a relaxation process corresponding to the above phenomena. The permittivity data analyzed using HN and Kohlrausch-Williams-Watta (KWW) functions show non-Debye relaxation processes and enhancement in the trans phase (enhanced solvent dynamics) as a function of salt concentration and temperature.
Computer simulation of the dynamics of the plastic phase of succinonitrile
The complex dynamics of the plastic phase of crystalline succinonitrile CN–CH2–CH2–CN, involving trans–gauche isomerization as well as molecular reorientations along the diagonals of the cubic unit cell, is investigated by means of molecular dynamics simulation. A simple molecular model in which the end CN groups and the CH2 groups are represented by single pseudoatoms is proposed. The model includes, in addition to the external degrees of freedom, three degrees of internal freedom described by two bending and a torsion coordinate. The intermolecular interactions are treated in terms of Lennard‐Jones potentials. Force constants are used for the bending coordinates and the intramolecular torsion is described by a two minima potential function with three parameters. The dynamical properties of the crystal are investigated by calculation of the time dependence of single molecule autocorrelation functions. It is found that the most suitable autocorrelation functions are those involving the torsion and the ori...