Measurement of the field dependent electrophoretic mobility of surface modified silica/AOT suspensions

We have investigated the electrophoretic mobility of silica spheres in a silica/AOT/paraffin ternary system as a function of the applied electric field and observed a large discrepancy with data published on a similar system ( Jin, F. H. ; Davis, H. T. ; Evans, D. F. Int. Conf. Digital Printing Technol. 1998, 206-209 ). We attribute the discrepancy to an artifact in the measurement technique used to obtain that published data. We believe the artifact is caused by high velocity particles being "swept" from the measurement volume, thereby biasing the result toward lower mobilities. Thus, the published measurements appear to indicate a high field plateau in mobility data around 500 kV/m. Our results indicate that the silica/AOT/paraffin solution is reaching dielectric breakdown prior to a conclusive high field plateau being unambiguously measured. At low field the mobility is in general agreement with the prior work ( Jin, F. H. ; Davis, H. T. ; Evans, D. F. Int. Conf. Digital Printing Technol. 1998, 206- 209 ). Any proposed models of apparent charging of particles which utilize the presence of a high field plateau are inappropriate unless the high field plateau is clearly established. Our work indicates that caution is required regarding the measurement of electrophoretic mobility at high electric fields.