A first-principles approach to electromechanics in liquids

Area of Science:

• Physics
• Physical Chemistry
• Fluid Dynamics

Background:

• Electromechanics in fluids governs liquid response to electric fields, crucial for controlling fluid behavior.
• Continuum theories suffice for macroscopic systems but fail at small scales relevant to biological and microfluidic systems.
• Existing models struggle with length scales comparable to natural correlation lengths in fluids.

Purpose of the Study:

• To present a first-principles theory for electromechanical phenomena in fluids.
• To address limitations of continuum approaches at small length scales.
• To provide a framework for understanding and controlling fluid behavior via electric fields.

Main Methods:

• Developed a theory based on hyper-density functional theory (hyper-DFT).
• Treated charge density as an observable, with free energy dependent on density and electrostatic potential.
• Derived coupling expressions between number and charge densities naturally within the formalism.

Main Results:

• The hyper-DFT formalism naturally incorporates couplings between number and charge densities.
• Avoided the need for empirical, spatially varying material parameters like the dielectric constant.
• Established a link between hyper-DFT and local molecular field theory for practical applications.

Conclusions:

• The new theory offers a robust framework for electromechanical phenomena in fluids, especially at small scales.
• It simplifies modeling by avoiding complex material parameterization.
• Facilitates machine learning applications for accurate free energy functional representations.