Plenary

Near-wall measurements in electroosmotic flow and inside the diffuse electric double layer

Reza Sadr, Minami Yoda

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Electroosmosis, where ions in a conducting fluid are driven by an electric field, is commonly used in microfluidics to drive aqueous electrolyte solutions. Strictly speaking, however, the electric field only drives the flow within the electric double layer next to the charged wall. Under appropriate conditions, the fluid velocity and the perturbation electric potential (compared with the wall ζ-potential) are proportional, i.e., similar, in electroosmotic flow. In this talk, we describe a novel technique, nano-particle image velocimetry, using evanescent-wave illumination, that can measure velocities, and hence changes in ζ-potential, within 250 nm of the wall. Mobilities were measured for the electroosmotic flow of sodium tetraborate buffers at molar concentrations C = 20 μM to 36 mM through 5-25 μm channels. In all cases, the results are in very good agreement with analytical predictions. Comparisons with analytical predictions at the two lowest concentrations of 20 μM and 36 μM suggest that the velocity data are obtained inside the double layer. These results are believed to be the first experimental measurements inside the diffuse electric double layer in electroosmotic flow of an aqueous solution. This work demonstrates that the Debye length underestimates the double layer thickness by up to an order of magnitude over a thousand-fold variation in ionic strength - and suggests that the double layer is accessible using current diagnostic techniques. At higher concentrations, the mobility decreases with increasing concentration, following a power-law relation. At C = 20 μM and 36 μM, however, mobility increases with concentration, even after correcting the experimentally obtained mobility values to reflect bulk velocity values.

Original languageEnglish
Title of host publication05AIChE: 2005 AIChE Annual Meeting and Fall Showcase, Conference Proceedings
Pages12726
Number of pages1
Publication statusPublished - 2005
Externally publishedYes
Event05AIChE: 2005 AIChE Annual Meeting and Fall Showcase - Cincinnati, OH, United States
Duration: 30 Oct 20054 Nov 2005

Other

Other05AIChE: 2005 AIChE Annual Meeting and Fall Showcase
CountryUnited States
CityCincinnati, OH
Period30/10/054/11/05

Fingerprint

Electric fields
Electroosmosis
Sodium borate
Fluids
Ionic strength
Microfluidics
Velocity measurement
Lighting
Electrolytes
Ions
Electric potential

ASJC Scopus subject areas

  • Engineering(all)

Cite this

Sadr, R., & Yoda, M. (2005). Plenary: Near-wall measurements in electroosmotic flow and inside the diffuse electric double layer. In 05AIChE: 2005 AIChE Annual Meeting and Fall Showcase, Conference Proceedings (pp. 12726)

Plenary : Near-wall measurements in electroosmotic flow and inside the diffuse electric double layer. / Sadr, Reza; Yoda, Minami.

05AIChE: 2005 AIChE Annual Meeting and Fall Showcase, Conference Proceedings. 2005. p. 12726.

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Sadr, R & Yoda, M 2005, Plenary: Near-wall measurements in electroosmotic flow and inside the diffuse electric double layer. in 05AIChE: 2005 AIChE Annual Meeting and Fall Showcase, Conference Proceedings. pp. 12726, 05AIChE: 2005 AIChE Annual Meeting and Fall Showcase, Cincinnati, OH, United States, 30/10/05.
Sadr R, Yoda M. Plenary: Near-wall measurements in electroosmotic flow and inside the diffuse electric double layer. In 05AIChE: 2005 AIChE Annual Meeting and Fall Showcase, Conference Proceedings. 2005. p. 12726
Sadr, Reza ; Yoda, Minami. / Plenary : Near-wall measurements in electroosmotic flow and inside the diffuse electric double layer. 05AIChE: 2005 AIChE Annual Meeting and Fall Showcase, Conference Proceedings. 2005. pp. 12726
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