Dynamic density functional theory of polymers with salt in electric fields

Area of Science:

• Materials Science
• Physical Chemistry
• Statistical Mechanics

Background:

• Polymer electrolytes are crucial for energy storage devices, but their ion transport mechanisms are complex.
• Understanding the local structure and dielectric properties is key to optimizing ion conductivity.
• Existing models often lack a direct link between microscopic structure and macroscopic transport phenomena.

Purpose of the Study:

• To develop a dynamic density functional theory (dDFT) for polymer electrolytes under applied electric fields.
• To establish connections between theoretical transport coefficients and experimental measurements.
• To investigate the influence of dielectric inhomogeneity on phase separation in polymer electrolytes.

Main Methods:

• Utilized linear irreversible thermodynamics to derive time-dependent equations for electrostatic potential and species volume fractions.
• Employed a field-theoretic description of free energy for salt-doped polymer melts, accounting for dielectric function variations.
• Related phenomenological Onsager transport coefficients to mutual diffusion, ionic conductivity, and transference numbers.

Main Results:

• The dDFT successfully models the effects of electric fields on polymer electrolyte local structure.
• Established connections between the theory's transport coefficients and experimental observables (diffusion, conductivity, transference).
• The steady-state limit revealed insights into dielectric inhomogeneity effects on phase separation.

Conclusions:

• The developed dDFT provides a framework for linking molecular structure to ion transport in polymer electrolytes.
• The theory bridges the gap between fundamental models and experimental validation.
• This work facilitates the development of multi-scale models for advanced material design.