Electrophoretic mobility does not always reflect the charge on an oil droplet

Knecht, V., Risselda, H. J., Mark, A. E. and Marrink, S. J. (2008) Electrophoretic mobility does not always reflect the charge on an oil droplet. Journal of Colloid and Interface Science, 318 2: 477-486. doi:10.1016/j.jcis.2007.10.035

Author Knecht, V.
Risselda, H. J.
Mark, A. E.
Marrink, S. J.
Title Electrophoretic mobility does not always reflect the charge on an oil droplet
Journal name Journal of Colloid and Interface Science   Check publisher's open access policy
ISSN 0021-9797
Publication date 2008-02-15
Year available 2007
Sub-type Article (original research)
DOI 10.1016/j.jcis.2007.10.035
Volume 318
Issue 2
Start page 477
End page 486
Total pages 10
Place of publication United States of America
Publisher Academic Press
Collection year 2008
Language eng
Subject 250403 Electroanalytical Chemistry
250303 Physical Organic Chemistry
780103 Chemical sciences
Abstract Electrophoresis is widely used to determine the electrostatic potential of colloidal particles. Oil droplets in pure water show negative or positive electrophoretic mobilities depending on the pH. This is commonly attributed to the adsorption of hydroxyl or hydronium ions, resulting in a negative or positive surface charge, respectively. This explanation, however, is not in agreement with the difference in isoelectric point and point of zero charge observed in experiment. Here we present molecular dynamics simulations of oil droplets in water in the presence of an external electric field but in the absence of any ions. The simulations reproduce the negative sign and the order of magnitude of the oil droplet mobilities at the point of zero charge in experiment. The electrostatic potential in the oil with respect to the water phase, induced by anisotropic dipole orientation in the interface, is positive. Our results suggest that electrophoretic mobility does not always reflect the net charge or electrostatic potential of a suspended liquid droplet and, thus, the interpretation of electrophoresis in terms of purely continuum effects may need to be reevaluated.
Keyword Electrophoresis
Electrokinetic phenomena
Zeta potential
Water structure
Molecular dynamics
Computer simulation
Q-Index Code C1
Q-Index Status Confirmed Code

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Created: Thu, 08 May 2008, 13:27:47 EST by Darryl Greensill on behalf of School of Chemistry & Molecular Biosciences