Effect of moisture on the dielectrophoretic spectra of glass spheres

Variable-frequency measurements (from 10 to 10⁵ Hz) on individual glass particles (~50 μm diameter) were performed, using an automated computer-controlled dielectrophoretic levitator. The particles were suspended in silicone oil after either of two treatments: long-term exposure to a water-saturated atmosphere, or drying in a low temperature oven (~250°C). The moisture treatment caused in increase of several orders of magnitude in the Maxwell-Wagner polarization relaxation frequency. Heat drying was observed to decrease any Maxwell-Wagner relaxation below the 10 Hz limit of the levitator. Uncertainties about the interrelationship of surface adsorption of water by the glass particles and the dissolved water content of the silicone oil exist, but it seems that the relaxation frequency shifts are due to changes in water concentration at the glass/water interface. The measurement capability demonstrated has implications with respect to the controversy surrounding the influence of moisture content on the performance of electrorheological fluids