Electro-optics of plate-like silica particle suspension

We focused on square plate-like silica particle, i.e., H+-exchanged ilerite (H-ilerite). On the basis of the characteristics of ion concentration polarization and relaxation in asymmetric electrical double layer (EDL) around H-ilerite platelets, electro-optics of H-ilerite suspensions was characterized. The responses of H-ilerite suspension to electric field were assessed by impedance dispersion, microscopic observation and electro-optics optical transmittance of light with the wavelength of 550 nm. As electric field is increased, the relaxation frequency of EDL polarization for H-ilerite systematically shifted from 480 Hz (random orientation) to 126 Hz (alignment to electric field). When electric field of 141 V-rms/cm and 10 kHz was switched on, transmittance decreased instantaneously. It was also observed that H-ilerite platelets were individually aligned to electric field in dilute suspension, followed by the formation of face-to-face aggregations of the platelets in concentrated suspension in the presence of AC electric field. When large aggregations were formed, the transmittance change in electro-optics was remarkably enhanced. When electric field was switched off, the transmittance showed fast and slow relaxations. The fast one corresponds to the rotary Brownian diffusion and becomes slow with increasing the volume fraction. The slow one can be related to the release of face-to-face aggregations. (C) 2012 Elsevier B.V. All rights reserved.