Importance of Multiple Ionic Species on the Diffusiophoresis of a Rigid, Charged-Regulated, Zwitterionic Sphere

The importance of the presence of multiple ionic species in the liquid phase on the diffusiophoresis of a charged-regulated, zwitterionic, rigid sphere is investigated. This analysis extends previous ones, where only two kinds of ionic species were assumed to present and a particle is maintained at either constant surface potential or constant surface charge, to a more general and realistic case. We show that the diffusiophoretic behavior of the particle is influenced significantly by the solution pH, the thickness of double layer, the strength of the applied salt concentration, and both the number and the type of ionic species. In particular, because both H+ and OH- are polarized by the electrical field arising from the applied salt concentration gradient, the strength of that electrical field is reduced accordingly. This effect is especially important when pH is either very high or very low. In addition, assuming the presence of only two kinds of ionic species can yield appreciable deviation, especially when the salt concentration is low.