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Concentration-Polarization Electroosmosis near Insulating Constrictions within Microfluidic Channels
Raúl Fernández-Mateo1, Víctor Calero2, Hywel Morgan1
1School of Electronics and Computer Science, University of Southampton, Southampton SO17 1BJ, United Kingdom.
Analytical Chemistry
|October 27, 2021
Summary
Concentration-polarization electroosmosis (CPEO) describes fluid flow around constrictions in microfluidic devices. This phenomenon, observed in shallow channels, can be mistaken for insulator-based-dielectrophoresis (iDEP) particle trapping.
Area of Science:
- Microfluidics
- Electrokinetics
- Surface Chemistry
Background:
- Microfluidic devices commonly use electric fields for particle manipulation.
- Insulator-based-dielectrophoresis (iDEP) relies on nonhomogeneous electric fields at constrictions for trapping.
- Electroosmotic flows (EOFs) are crucial in microfluidic transport phenomena.
Purpose of the Study:
- To describe stationary electroosmotic flows around insulating constrictions under AC electric fields.
- To investigate the phenomenon termed concentration-polarization electroosmosis (CPEO).
- To analyze the influence of channel height on CPEO and particle trapping.
Main Methods:
- Experimental characterization of EOFs in microfluidic channels (50 and 10 μm heights).
- Numerical simulations using an electrokinetic model.
- Incorporation of surface conductance effects on charged insulating walls into the model.
Main Results:
- Observed stationary electroosmotic flows around insulating constrictions induced by low-frequency AC fields.
- Model predictions showed qualitative agreement with experimental flow characteristics.
- Particle trapping observed in shallow channels (10 μm), potentially mimicking iDEP.
Conclusions:
- CPEO is a significant fluid behavior in microfluidic constrictions under AC fields.
- Surface conductance plays a key role in modifying ionic concentration and EOFs.
- The observed particle trapping in shallow channels may be misinterpreted as iDEP, highlighting the complexity of particle manipulation in microfluidics.
