Symmetric diffusion equations, barodiffusion, and cross-diffusion in concentrated liquid mixtures

Area of Science:

• Physical Chemistry
• Chemical Engineering
• Thermodynamics

Background:

• Current diffusion models for multicomponent mixtures are often asymmetric and rely on arbitrary solvent selection.
• This leads to interpreter-dependent experimental data analysis, especially in concentrated mixtures.

Purpose of the Study:

• To derive a symmetric system of diffusion equations for multicomponent mixtures.
• To incorporate secondary pressure gradients, barodiffusion, and diffusiophoresis into diffusion modeling.
• To apply the new model to a binary mixture and compare predictions with standard theory.

Main Methods:

• Derivation of a symmetric system of diffusion equations using a spontaneously produced secondary pressure gradient.
• Introduction of barodiffusion (force = secondary pressure gradient × molecular volume).
• Inclusion of diffusiophoresis due to hydrodynamic stresses from concentration gradients.

Main Results:

• The new model predicts lower concentration gradients in binary mixtures compared to standard theories.
• The concentration dependence of the effective diffusion coefficient differs from standard predictions.
• The model was applied to a benzene and 1,2-dichloroethane mixture under a uniform force field.

Conclusions:

• The developed symmetric diffusion model offers a new perspective on multicomponent mixture behavior.
• The findings suggest potential for more accurate interpretation of experimental diffusion data.
• Proposed experiments aim to validate the new model against existing theoretical frameworks.