Dielectric relaxation of polymers

This is an example of evaluating dielectric relaxation properties of polymer materials by Molecular Dynamics (MD) simulations. Specifically, the autocorrelation function of the dipole moment of cis-polybutadiene was analyzed and fitted with the KWW equation to determine relaxation time. Furthermore, the relaxation time was evaluated as a function of temperature, and the dielectric relaxation spectrum was derived by Fourier transformation. This allows theoretical prediction of the frequency response of materials.

Use Cases Highlights

Evaluation of dielectric relaxation from polymer MD simulations
Analysis of dielectric response from polymer relaxation behavior
Capability to evaluate complex permittivity

Evaluation of dielectric relaxation from polymer MD calculations

The dipole moment autocorrelation function Φ of cis-polybutadiene at various temperatures and its fitting with the KWW equation are shown. Relaxation becomes slower with decreasing temperature, and the KWW fit enables quantitative evaluation of relaxation times.

Autocorrelation function Φ at each temperature and fitting results with KWW equation

Analysis of dielectric response from polymer relaxation behavior

A graph plotting relaxation time τ calculated from fitting to the KWW equation against the inverse of temperature is shown. This plot demonstrates that relaxation time changes exponentially with temperature, aiding in the understanding of glass transition behavior. Comparisons with data from previous literature are also included.

Relaxation time τ [ps] obtained from KWW fitting plotted against the inverse of temperature

Evaluation of complex dielectric constant

The real and imaginary parts of the dielectric relaxation spectrum obtained by Fourier transforming the autocorrelation function from the KWW equation are shown. This spectrum represents the frequency response characteristics of the material and is used to evaluate the frequency dependence of dielectric loss and permittivity. Comparison with experiments also confirms the model's validity.