Field dependence of the electrophoretic mobility of particles suspended in low-conductivity liquids

Abstract

An experimental arrangement is described for the determination of the electrophoretic mobility of suspended particles as a function of particle size. While sedimenting between plane vertical electrodes the particles were deflected to and fro by short rectangular field pulses. Results of polystyrene spheres suspended in isodecane with oil-soluble ionic additives as stabilizers are reported. The field dependence of the mobility at higher conductivity (10 −10 … 10 −9 Ω −1 m −1) and medium field strength (5 × 10 4 … 5 × 10 5 V/m) is interpreted as a partial decoupling of the particles from their diffuse electric double layer. At low conductivity and high field strength, when the double layer is completely stripped off, the charge of the particle can be calculated directly by equating the Coulomb and Stokes forces. The ratio between constant low-field (intact double layer) and constant high-field mobility (1:8) is in good agreement with theoretical calculations.