Eur. Phys. J. E 7, 371-379 (2002)
DOI: 10.1140/epje/i2001-10102-y
Electrophoresis of a charge-inverted macroion complex: Molecular-dynamics study
Motohiko Tanaka1 and A.Yu. Grosberg21 National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan
2 Department of Physics, University of Minnesota, Minneapolis, MN 55455, USA
mtanaka@nifs.ac.jp
(Received 5 December 2001 and Received in final form 10 April 2002)
Abstract
We have performed molecular-dynamics simulations to
study the effect of an external electric field on a macroion in
the solution of multivalent
Z:1 salt. To obtain plausible
hydrodynamics of the medium, we explicitly make the simulation
of many neutral particles along with ions. In a weak
electric field, the macroion drifts together with the strongly
adsorbed multivalent counterions along the electric field, in
the direction proving inversion of the charge sign. The
reversed mobility of the macroion is insensitive to the external
field, and increases with salt ionic strength. The reversed
mobility takes a maximal value at intermediate counterion valence.
The motion of the macroion complex does not induce any flow of the
neutral solvent away from the macroion, which reveals screening of
hydrodynamic interactions at short distances in electrolyte
solutions. A very large electric field, comparable to the
macroion unscreened field, disrupts charge inversion by stripping
the adsorbed counterions off the macroion.
61.25.Hq - Macromolecular and polymer solutions; polymer melts; swelling.
82.45.-h - Electrochemistry and electrophoresis.
82.20.Wt - Computational modeling; simulation.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2002
