Determination of the Zeta Potential of Porous Substrates by Droplet Deflection: II. Generation of Electrokinetic Flow in a Nonpolar Liquid

Here we study the nature and extent of free electrical charges in nonpolar liquids, using a recently introduced technique of observing droplet deflection generated by electrokinetic flow in a porous substrate. In the presence of dispersed water, surfactant molecules agglomerate and inverted micelles...

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Bibliographic Details
Published in:Langmuir 2010-03, Vol.26 (5), p.3126-3133
Main Authors: Barz, Dominik P. J, Vogel, Michael J, Steen, Paul H
Format: Article
Language:English
Subjects:
Chemistry
Colloidal state and disperse state
Colloids: Surfactants and Self-Assembly, Dispersions, Emulsions, Foams
Exact sciences and technology
General and physical chemistry
Micelles. Thin films
Porous materials
Surface physical chemistry
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Summary:Here we study the nature and extent of free electrical charges in nonpolar liquids, using a recently introduced technique of observing droplet deflection generated by electrokinetic flow in a porous substrate. In the presence of dispersed water, surfactant molecules agglomerate and inverted micelles are generated which may act as charge carriers. In the present work, the conductivities of solutions of a nonpolar liquid with several concentrations of a dissolved surfactant are measured by electrical transients. The induced current densities are proportional to the applied voltage, indicating that the solutions represent an ohmic system. The conductivity does not scale simply with the surfactant concentration, though. It is inferred that different micellization mechanisms exist depending on the surfactant concentration, and a model is sketched. Further experiments reveal that flows of such solutions can be generated within saturated porous substrates when they are subjected to moderate electric fields. An investigation of the phenomena leads to the conclusion that these flows exist due to the presence of an electrical double layer; that is, they are of electrokinetic (electroosmotic) origin. Hence, the measured electrokinetic flow rates can be related to the zeta potential of the porous substrate saturated with the solution. Plotting the zeta potential against the logarithm of the ionic strength reveals a linear relationship.
ISSN:0743-7463
1520-5827
DOI:10.1021/la903075w