Electric response of nonspherical and spherical silica particle dispersions to ac electric field.

For the purpose of revealing unique aspects of the electrical double layer (EDL) around nonspherical particles, we focus on a silica square platelike particle with well-defined shape, i.e., H-ilerite. Impedance measurements for suspensions of silica spherical and square platelike particles are performed to examine ion concentration polarization and its relaxation in their EDLs under ac electric fields that are high enough to orient H-ilerite to electric fields and form pearl chains of particles. For a silica spherical particle, the relaxation frequency of ion concentration polarization in EDL around the particles is independent of applied electric field strength and the volume fraction of the particles in suspension. The conductance ratios of silica particle suspension to its supernatant show a good linear relation against the volume fraction independently of applied electric field strength. For H-ilerite, at low electric field strength where there is neither electric orientation nor pearl chain formation, the conductance ratio also shows a linear relation against the volume fraction. The slope of the conductance ratio to the volume fraction increases and the relaxation frequency decreases as applied electric field strength increases. In addition, two linear relations with different slopes, where the slope becomes steep at higher volume fractions, appear in the plots of the conductance ratio against the volume fraction. Such a unique response of H-ilerite suspension to electric field can be explained by the electric orientation of H-ilerite accompanying pearl chain formation.