Kavli Affiliate: Jos Zwanikken
| First 5 Authors: Jos Zwanikken, René van Roij, , ,
| Summary:
Within a modified Poisson-Boltzmann theory we study the effect of Bjerrum
pairs on the typical length scale $1/bar{kappa}$ over which electric fields
are screened in electrolyte solutions, taking into account a simple
association-dissociation equilibrium between free ions and Bjerrum pairs. At
low densities of Bjerrum pairs, this length scale is well approximated by the
Debye length $1/kappapropto 1/sqrt{rho_mathrm{s}}$, with $rho_mathrm{s}$
the free ion density. At high densities of Bjerrum pairs, however, we find
$1/bar{kappa}propto sqrt{rho_mathrm{s}}$ which is significantly larger
than $1/kappa$ due to the enhanced effective permittivity of the electrolyte,
caused by the polarization of Bjerrum pairs. We argue that this mechanism may
explain the recently observed anomalously large colloid-free zones between an
oil-dispersed colloidal crystal and a colloidal monolayer at the oil-water
interface.
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