  In this paper we develop a simple theory to study the effects of ionic size
on ionic distributions around a charged spherical particle. We include a
correction to the regular Poisson-Boltzmann equation in order to take into
account the size of ions in a mean-field regime. The results are compared with
Monte Carlo simulations and a Density Functional Theory based on the
Fundamental Measure approach and a second-order bulk expansion which accounts
for electrostatic correlations. The agreement is very good even for multivalent
ions. Our results show that the theory can be applied with very good accuracy
in the description of ions with high effective ionic radii and low
concentration, interacting with a colloid or nanoparticle in an electrolyte
solution.
