Onsager's reciprocal relations in electrolyte solutions. I. Sedimentation and electroacoustics

Area of Science:

• Physical Chemistry
• Thermodynamics
• Electrochemistry

Background:

• Coupled transport phenomena in electrolyte solutions are complex.
• Understanding ion dynamics under external fields is crucial.
• Previous models for electroacoustic phenomena lacked a unified thermodynamic basis.

Purpose of the Study:

• To establish a mathematical equivalence between sedimentation current and ionic vibration current.
• To investigate coupled transport phenomena using both irreversible thermodynamics and a mechanical framework.
• To reconcile theoretical frameworks for ion dynamics in electrolyte solutions.

Main Methods:

• Application of irreversible thermodynamics.
• Analysis of mass fluxes in a chosen reference frame for electroacoustics.
• Development of a mechanical framework using Newtonian equations for charged solutes.

Main Results:

• Demonstrated mathematical equivalence between sedimentation current and low-frequency ionic vibration current.
• Showed that ideal mechanical framework results satisfy Onsager's reciprocal relations.
• Derived conditions for corrective forces to maintain Onsager relations with ionic interactions.

Conclusions:

• Sedimentation and electroacoustic phenomena share a fundamental thermodynamic link.
• The mechanical framework provides a valid approach for studying ion dynamics.
• No additional diffusion term is required in solute flux, even with concentration gradients, simplifying transport models.