Volume 46, Number 4, May II 1999
|Page(s)||454 - 460|
|Section||Atomic and molecular physics|
|Published online||01 September 2002|
Spontaneous overcharging of macro-ion complexes
Department of Chemistry and Biochemistry,
University of California
Los Angeles, CA 90095, USA
2 Department of Physics, University of California Los Angeles, CA 90095, USA
Accepted: 1 March 1999
Oppositely charged macro-ions—one of which is flexible and carries a larger total charge than the other—are expected on an energetic basis to assemble into neutral complexes which can aggregate due to attractive (e.g., van der Waals) interactions. We treat in this paper the counter-intuitive appearance of spontaneous overcharging in polyelectrolyte-colloid complexes, a phenomenon which has been observed in experiments and simulations involving flexible chains adsorbing on oppositely charged cores. We show that this overcharging can be accounted for in the Poisson-Boltzmann approximation; within this theory, overcharging is an entropic effect associated with release of the counterions of the highly charged polyelectrolyte chain as it "overwinds” onto the rigid colloidal particle. Increasing the rigidity of the polyelectrolyte chain leads eventually to undercharging of the complex.
PACS: 36.20.-r – Macromolecules and polymer molecules / 87.10.+e – Biological and medical physics: General theory and mathematical aspects / 87.15.Nn – Properties of solutions; aggregation and crystallization of macromolecules
© EDP Sciences, 1999
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