Towards local deposition of particles by electrophoresis in dc electric fields in polar and nonpolar media and mixtures thereof

As a step towards the understanding of local electrophoretic deposition, particle trajectories are investigated in nonuniform electric field. Our hypothesis is that particles can be locally deposited in nonuniform fields. As an important process parameter, we also study the effect of solvent polarity. For the experiments, the particles are coated with suitable dispersants. The movement and deposition in polar as well as in nonpolar media and mixtures thereof in nonuniform dc electric fields are monitored by optical microscopy. We find that the average velocity of particles in pure cyclohexane increases linear with electric field strength in agreement with standard theory. Electrophoretic mobility and Zeta potential of the particles are calculated from this data. The particles deposit in a homogeneous layer on the electrode surface. The same findings are true for mixtures of 7.5 vol% to 30 vol% ethanol in cyclohexane as suspension media. In water, the particles move against the apparent electrostatic force at voltages below 3 V and do not deposit on either electrode. At voltages above 3 V dendritic structures are formed by cathodic electrophoretic deposition. We conclude that under suitable conditions, local deposition of particles is possible.