Charged particles at fluid interfaces as a probe into structural details of a double layer

Abstract

Electrostatic interactions between charged, distant colloids in a bulk electrolyte solution do not depend on the inherent structure of ions and a solvent forming a double layer. For charged colloids trapped at an interface between an electrolyte and air this no longer holds; as the electrostatic interactions are mediated via air and the field lines determining the interactions originate at the charged surface, these details come into prominence. Using the Langevin–Poisson–Boltzmann equation we investigate how steric effects and the polarization saturation of a solvent effect the contact potential at the colloid surface and, in consequence, the long range interactions between colloids trapped at an interface. For a surface charge 0.4 C m⁻² the combination of these effects can increase the interactions by up to ∼40 times when compared to Poisson–Boltzmann calculations. The validity of these enhancement mechanisms is supported by recent experimental data (K. Masschaele et al., Phys. Rev. Lett., 2010, 105, 048303).