The Electric Double Layer Structure Around Charged Spherical Interfaces
  We derive a formally simple approximate analytical solution to the Poisson-Boltzmann equation for the spherical system via a geometric mapping. Its regime of applicability in the parameter space of the spherical radius and the surface potential is determined, and its superiority over the linearized solution is demonstrated. 
Zhenwei Yao, Mark J. Bowick and Xu Ma
cond-mat.soft cond-mat.mes-hall cond-mat.mtrl-sci