Optical Properties of Nonaqueous Suspensions in Electric Fields

The optical properties of suspensions consisting of pigmented shell/polymer core composite particles dispersed in a silicone oil were studied in electric fields. In the absence of electric fields, the transmittance shows an exponential decay with sample thickness and particle concentration. The particles may be randomly dispersed in the medium. The application of electric field leads to an increase in the transmittance of suspensions. The clearing effect is very striking, especially for concentrated suspensions in a thick cell. In electric fields, the transmittance is almost independent of thickness in the range 0.15-1.1 mm and linearly decreases with increasing particle concentration. Microscopic observation shows that many discrete clusters are formed in electric fields. Based on the analysis of dipole-dipole interactions, the clusters may be composed of fully developed chains spanning the electrodes. Since the columns are aligned in the direction parallel to the optical path, the transmittance is not affected by the cell thickness. In addition, because of the increase in the cross section of the column, the transmittance shows a linear dependence on the particle concentration. The optical properties of suspensions can be explained by the column formation of particles in electric fields.