Measurement of electroosmotic and electrophoretic velocities using pulsed and sinusoidal electric fields

• Published in: Electrophoresis 2017-04, Vol.38 (7), p.1022-1037
• Main Authors: Sadek, Samir H., Pimenta, Francisco, Pinho, Fernando T., Alves, Manuel A.
• Format: Article
• Language: English
• Subjects: Channels; Computational fluid dynamics; Diffusion; Diffusion rate; Electric fields; Electricity; Electroosmosis - methods; Electroosmotic mobility; Electrophoresis; Electrophoresis - methods; Electrophoretic mobility; Exact solutions; Measurement methods; Microchannels; Microfluidic Analytical Techniques - methods; Models, Theoretical; Part III: Methodologies and Applications; Particle Size; Particle tracking; Particle tracking velocimetry; Polydimethylsiloxane; Polystyrene resins; Polystyrenes - chemistry; Rheology - methods; Temporal resolution; Tracer particles; Velocity measurement; Viscoelastic fluids; Viscoelasticity; Zeta‐potential measurement
• ISSN: 0173-0835; 1522-2683
• DOI: 10.1002/elps.201600368

In this work, we explore two methods to simultaneously measure the electroosmotic mobility in microchannels and the electrophoretic mobility of micron‐sized tracer particles. The first method is based on imposing a pulsed electric field, which allows to isolate electrophoresis and electroosmosis at the startup and shutdown of the pulse, respectively. In the second method, a sinusoidal electric field is generated and the mobilities are found by minimizing the difference between the measured velocity of tracer particles and the velocity computed from an analytical expression. Both methods produced consistent results using polydimethylsiloxane microchannels and polystyrene micro‐particles, provided that the temporal resolution of the particle tracking velocimetry technique used to compute the velocity of the tracer particles is fast enough to resolve the diffusion time‐scale based on the characteristic channel length scale. Additionally, we present results with the pulse method for viscoelastic fluids, which show a more complex transient response with significant velocity overshoots and undershoots after the start and the end of the applied electric pulse, respectively.