Electrophoretic movement of hollow silica particles under DC electric fields

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The electrophoretic movement of colloidal silica particles with hollow interior and nanoporous shell structure was examined under a homogeneous direct current (DC) electric field as a function of field strengths (50–150 V) and solution pHs (4–10). The electrophoretic behavior was compared with that of solid silica particles of similar size. In an acidic solution (pH ∼4) at which the solution pH near the PZC (pH ∼2), mobility of the hollow particles appeared to be insensitive to the change of applied voltage in a dilute solids concentration. As pH moved away from the PZC to a basic solution (pH ∼10), velocity of the charged particles increased pronouncedly and the velocity was in a linear proportion with the DC field strength, suggesting that the particles were moved by electrophoresis. The hollow silica particles yet showed a much slower electrophoretic velocity, less than one half, than that of the solid counterparts at the alkaline situation (pH ∼10). This lagged motion was due presumably to the rough outer surface and the permeable shell structure (pore radius ∼20 nm), both contributing to the hydrodynamic friction that retards the electrophoretic movement.
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