Reversed electrophoretic mobility of a spherical colloid in the Modified Poisson-Boltzmann approach Article uri icon

abstract

  • The electrophoretic mobility of a spherical colloid particle immersed in a binary electrolyte is studied by using the Primitive Model Electrophoresis formalism, in combination with the Modified Poisson-Boltzmann equilibrium theory. This approach differs from the classical descriptions of electrophoresis, based on the Poisson-Boltzmann equation for point ions, in that the Primitive Model Electrophoresis theory takes into account consistently the ionic correlations and excluded volume contributions due to the finite size of the ions. Using the equilibrium radial distribution functions of the Modified Poisson-Boltzmann, the primitive model electrophoresis theory predicts a non-universal behavior of the reduced mobility, as a function of the reduced ζ-potential, in contrast to the universal behavior exhibited by the well-known treatment of Wiersema, O%27Brien and White. The primitive model electrophoresis mobilities calculated with the Modified Poisson-Boltzmann theory compare favorably with the previously reported mobilities obtained through the hypernetted-chain/mean spherical approximation equilibrium theory. The agreement between these two theories is very good, both quantitatively and qualitatively for univalent electrolytes. For 2:2 electrolytes they qualitatively agree. In particular, the Modified Poisson-Boltzmann mobilities confirm the occurrence of reversed electrophoretic mobilities. Overall the results presented here show the adequacy of the Modified Poisson-Boltzmann equilibrium theory to calculate the electrophoretic mobility of colloidal particles. © 2016 Elsevier B.V.
  • The electrophoretic mobility of a spherical colloid particle immersed in a binary electrolyte is studied by using the Primitive Model Electrophoresis formalism, in combination with the Modified Poisson-Boltzmann equilibrium theory. This approach differs from the classical descriptions of electrophoresis, based on the Poisson-Boltzmann equation for point ions, in that the Primitive Model Electrophoresis theory takes into account consistently the ionic correlations and excluded volume contributions due to the finite size of the ions. Using the equilibrium radial distribution functions of the Modified Poisson-Boltzmann, the primitive model electrophoresis theory predicts a non-universal behavior of the reduced mobility, as a function of the reduced ζ-potential, in contrast to the universal behavior exhibited by the well-known treatment of Wiersema, O'Brien and White. The primitive model electrophoresis mobilities calculated with the Modified Poisson-Boltzmann theory compare favorably with the previously reported mobilities obtained through the hypernetted-chain/mean spherical approximation equilibrium theory. The agreement between these two theories is very good, both quantitatively and qualitatively for univalent electrolytes. For 2:2 electrolytes they qualitatively agree. In particular, the Modified Poisson-Boltzmann mobilities confirm the occurrence of reversed electrophoretic mobilities. Overall the results presented here show the adequacy of the Modified Poisson-Boltzmann equilibrium theory to calculate the electrophoretic mobility of colloidal particles. © 2016 Elsevier B.V.

publication date

  • 2017-01-01