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Updated: Jun 28, 2025
08:41
Generation and Control of Electrohydrodynamic Flows in Aqueous Electrolyte Solutions
Published on: September 7, 2018
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Diffusioosmotic flow reversals due to ion-ion electrostatic correlations.
Shengji Zhang1, Henry C W Chu2
1Department of Chemical Engineering, University of Florida, Gainesville, FL 32611, USA.
Nanoscale
|April 23, 2024
Summary
New theories reveal ion-ion electrostatic correlations cause unique diffusioosmosis flow reversals in concentrated electrolytes, differing from dilute solutions. This impacts applications like species separation and energy harvesting.
Area of Science:
- Physical Chemistry
- Electrochemistry
- Fluid Dynamics
Background:
- Existing diffusioosmosis theories overlook ion-ion electrostatic correlations, crucial for concentrated electrolytes.
- These correlations significantly influence ion behavior and fluid transport in confined systems.
Purpose of the Study:
- To develop a mathematical model for numerically computing diffusioosmotic mobilities in charged parallel-plate channels.
- To investigate the impact of ion-ion electrostatic correlations and finite ion size on diffusioosmosis across a range of electrolyte concentrations.
Main Methods:
- Utilized a modified Poisson equation to incorporate ion-ion electrostatic correlations.
- Employed the Bikerman model to account for the finite size of ions.
- Performed numerical computations for binary symmetric electrolytes in charged parallel-plate channels.
Main Results:
- Identified a unique diffusioosmosis flow reversal driven by ion-ion electrostatic correlations, not predicted by existing theories. This occurs at ≈0.4 M for monovalent and ≈0.003 M for divalent electrolytes.
- Predicted a second flow reversal due to competing chemiosmosis and electroosmosis, tunable by channel surface charge.
- Demonstrated that electrostatic correlations significantly alter the dependence of flow reversal on surface charge and ion diffusivity between concentrated and dilute electrolytes.
Conclusions:
- Diffusioosmosis in concentrated electrolytes can exhibit qualitatively different behavior (magnitude and direction) compared to dilute electrolytes due to ion-ion electrostatic correlations.
- The developed model provides a tool for designing diffusioosmosis processes for applications in species mixing/separation, enhanced oil recovery, and reverse electrodialysis.
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