Theoretical Prediction of Thermal Polarization.

Area of Science:

• Statistical Mechanics
• Soft Matter Physics
• Computational Chemistry

Background:

• The thermo-orientation effect in fluids leads to phenomena like thermally induced polarization and monopoles.
• Existing theories rely on phenomenological equations or scaling arguments, often requiring fitting parameters.
• A robust theoretical framework is needed to accurately predict and understand these nonequilibrium effects.

Purpose of the Study:

• To develop a parameter-free mean-field theory for the thermo-orientation effect in off-center Stockmayer fluids.
• To provide a theoretical explanation for recently predicted thermally induced polarization and monopoles.
• To elucidate the contributions of temperature and density gradients to nonequilibrium molecular alignment.

Main Methods:

• Formulation of a mean-field theory based on local equilibrium and an equation of state.
• Construction of an effective Hamiltonian for calculating local Boltzmann averages.
• Decomposition of molecular alignment into temperature and density gradient contributions.

Main Results:

• The theory accurately predicts molecular orientations, showing excellent agreement with simulation results.
• The approach does not necessitate any fitting parameters.
• The interplay between temperature and density gradients is shown to be crucial for the observed nonequilibrium alignment.

Conclusions:

• The developed mean-field theory offers a fundamental explanation for the thermo-orientation effect in Stockmayer fluids.
• This parameter-free approach provides a reliable tool for understanding and predicting fluid polarization phenomena.
• The study highlights the critical role of competing gradients in driving complex nonequilibrium behaviors in soft matter systems.