Impact of DC Electric Field Direction on Sedimentation Behavior of Colloidal Particles in Water

Colloidal particles in water exhibit increased sedimentation velocity under a horizontal DC electric field of several V/mm compared to no field. Hollow particles with a lower density than water show an increased ascent velocity with the horizontal electric field. These phenomena suggest that colloidal particles form flocs due to the electric field, known as the Electrically Induced Rapid Separation (ERS) effect. This study investigates, for the first time, the impact of the DC electric field direction on the ERS effect. The electric field was defined as horizontal when the inclination angle <i>θ</i> = 0° and vertical at <i>θ</i> = 90°, covering all inclination angles. Results showed that the ERS effect increased for <i>θ</i> < ~20-30° in both upward and downward directions. However, beyond this range, the ERS effect decreased or disappeared. At larger <i>θ</i> values, convection was observed, significantly improving colloidal particle dispersion stability. Additionally, negatively charged particles were observed to be "repelled" near the negative electrode. This study offers new insights into controlling particle dispersion stability using electric fields and suggests potential applications in colloid and material science.