title: Primary charge effects on prolate spheroids with moderate aspect ratios.
abstract: In this article, we investigate the behavior of charged spheroidal colloids with moderate aspect ratios in linear flow fields. We use direct numerical simulation with body-fitted grids for the solution of the Stokes-Poisson-Nernst-Planck system to include all non-linear effects. Therefore, we propose an efficient semi-implicit time discretization based on a splitting of the Stokes equation. We will study the effects of the electric double layer on the forces, torques and on the motion of spheroidal particles. For low Reynolds numbers, we find approximating linear expressions between the ambient fluid flow and the force and torque on the particle. The description of this linear behavior is based on the resistance functions, whose dependencies on the Debye length and the zeta potential are investigated. It is recovered that the resistance functions obey a quadratic dependence on the zeta potential in the small zeta potential regime. For low values of the zeta potential, approximate formulas for the resistance functions are given. The approximation properties are carefully studied by comparing the approximate results with direct numerical simulations. For the case of a shear flow, the approximate formulas can be used to avoid time-consuming direct numerical simulations.
authors.affiliation: Institute of Mechanical Process Engineering and Mechanics, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany. florian.keller@kit.edu
authors.forename: Florian
authors.initials: F
authors.lastname: Keller
authors.forename: Hermann
authors.initials: H
authors.lastname: Nirschl
authors.forename: Willy
authors.initials: W
authors.lastname: Dörfler
mesh_terms: D003102:Colloids / Q000737:chemistry*; D008863:Microspheres; D008956:Models, Chemical; D010316:Particle Size; D013499:Surface Properties
chemical_list: D003102:Colloids