| Abstract
| - Counterions in an electric double layer (EDL) around a colloidal particle accumulate on one side of the EDL andare deficient on the other side under an electric field, resulting in an imbalance of ionic concentration in the EDL,that is to say, the ionic polarization of EDL. It is well known that the ionic polarization of EDL induces electric dipolemoments whereby the alignments of colloidal particles (e.g., pearl chains) are formed under alternating electric fields.In this study, we focus on the effect of the frequency of applied electric fields (100 Hz−1 kHz) on the alignment ofsilica particles settling at the bottom of a silica glass vessel. In digital imaging analyses for pearl chains of silicaparticles, it is confirmed that surface distances between two neighboring particles decrease but the number of particlesin a pearl chain increases as the frequency of the applied electric field is lowered from 1 kHz to 100 Hz. Moreinterestingly, electrical conductance measurements suggest that the induced ionic polarization of EDL around silicaparticles at the bottom of the silica vessel is enhanced as the frequency is lowered from 1 kHz to 100 Hz, whereasthe ionic polarization around isolated silica particles in uniform dispersions is alleviated by the relaxation of ionicconcentration in the EDL as a result of the diffusion of counterions. This curious phenomenon can be explained byconsidering that the ionic polarization of EDL of silica particles at the bottom of a vessel is affected by the electro-osmosis of the silica surface at the bottom of the vessel.
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