Aspects of ionic diffusion through thick matrices of charged particles.

Area of Science:

• Physical Chemistry
• Materials Science
• Chemical Engineering

Background:

• Literature review reveals higher co-ion than counter-ion diffusivity, challenging electroneutrality.
• Existing studies often neglect the water of hydration carried by diffusing ions.
• Nernst and Donnan zones at membrane interfaces are typically not quantitatively analyzed.

Purpose of the Study:

• To critically review literature on ionic diffusion through charged matrices.
• To highlight the significance of ion-bound water transport and its impact.
• To quantitatively analyze Nernst and Donnan zones and assess bivalent salt effects.

Main Methods:

• Literature synthesis and critical analysis.
• Theoretical modeling of ion and water transport.
• Quantitative determination of Nernst layer and Donnan zone thicknesses using two methods.

Main Results:

• Observed co-ion diffusivity may indicate unanalyzed ions, necessitating complete chemical analysis.
• Ion-bound water transport can counteract osmotic water flow, with implications at critical concentrations.
• Identical Nernst layer and Donnan zone thicknesses were obtained via two distinct quantitative methods.
• Soluble bivalent salts can influence ion diffusivity, with some co-ions migrating upstream.

Conclusions:

• Complete chemical analysis of solutions is essential to avoid misleading inferences in ionic diffusion studies.
• The role of ion-bound water transport in ionic diffusion requires further attention.
• Quantitative analysis of interfacial layers provides a more accurate understanding of ion transport phenomena.
• Bivalent salts introduce complexities in ion diffusion, affecting co-ion and counter-ion movement.