Original scientific paper

https://doi.org/10.5562/cca1824

Attraction between Like Charged Surfaces Mediated by Uniformly Charged Spherical Colloids in a Salt Solution

Sylvio May ; Department of Physics, North Dakota State University, Fargo ND, 58108-6050, USA
Klemen Bohinc ; Faculty of Health Sciences, University of Ljubljana, SI-1000 Ljubljana, Slovenia

Abstract

Like-charged macromolecules repel in electrolyte solutions that contain small (i.e. point-like)
monovalent co- and counterions. Yet, if the mobile ions of one species are spatially extended instead of
being point-like, the interaction may turn attractive. This effect can be captured within the mean-field
Poisson-Boltzmann framework if the charge distribution within the spatially extended ions is accounted
for. This has been demonstrated recently for rod-like ions. In the present work, we consider an electrolyte
solution that is composed of monovalent point-like salt ions and uniformly charged spherical colloids,
sandwiched between two planar like-charged surfaces. Minimization of the mean-field free energy yields
an integral-differential equation for the electrostatic potential that we solve numerically within the linear
Debye-Hückel limit. The free energy, which we calculate from the potential, indeed predicts attractive interactions
for sufficiently large spherical colloids. We derive an approximate analytical expression for the
critical colloid size, above which attraction between like-charged surfaces starts to emerge. (doi:
10.5562/cca1824)

Keywords

Poisson-Boltzmann; ionic interactions; electrostatics; colloids; electrolyte

Hrčak ID:

71988

URI

https://hrcak.srce.hr/71988

Publication date:

3.10.2011.

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