Volume 88, Number 1, October 2009
Article Number 14003
Number of page(s) 6
Section Electromagnetism, Optics, Acoustics, Heat Transfer, Classical Mechanics, and Fluid Dynamics
Published online 26 October 2009
EPL, 88 (2009) 14003
DOI: 10.1209/0295-5075/88/14003

Poisson-Boltzmann model in a solvent of interacting Langevin dipoles

D. H. Mengistu1, K. Bohinc2 and S. May1

1   Department of Physics, North Dakota State University - Fargo, ND 58108-6050, USA
2   Faculty of Health Sciences, University of Ljubljana - Poljanska 26a, 1000 Ljubljana, Slovenia, EU

received 7 August 2009; accepted in final form 29 September 2009; published October 2009
published online 26 October 2009

We incorporate a solvent model of interacting Langevin dipoles into the Poisson-Boltzmann formalism of mobile point-like ions close to a single charged surface. Our model aims at understanding the interplay between the diffuse double layer and the polarization of water due to a surface-induced dipolar ordering. We account for interactions between the Langevin dipoles, which leads to an intrinsic spatial decay length of the solvent polarization. An analytical solution of the free energy in the weak perturbation limit is presented and compared with the nonlinear regime. From our analytical results we derive conditions for the optimal polarization at the surface and for the sign inversion of the electrostatic potential.

41.20.Cv - Electrostatics; Poisson and Laplace equations, boundary-value problems.
87.85.J- - Biomaterials.

© EPLA 2009