Dielectric properties of nanopowder emulsions in paraffin oil

This work investigates polarization phenomena induced by nanoparticle inclusions in paraffin oil, an insulating organic liquid. Fine metal oxide powders and nanopowders of Al₂O₃, TiO₂, CuO, Cu₂O and Fe₂O₃ were tested at concentrations up to 5% w/v in the liquid matrix. Emulsification was attained by ultrasound treatment. The relative dielectric constant and loss tangent (tand) of both pure oil and emulsions were recorded in the 20 Hz-1 MHz frequency range. Results depend both on grain size and on the specific compound. In the case of alumina nanoparticles, dielectric behavior is dominated by grain surface polarization phenomena induced by adsorbed water. This effect can be partially cancelled out by the addition of titania nanoparticles. Titanium and (to a lesser extent) ferric oxide increased the dielectric constant at middle and high frequencies. Copper (I) and (II) oxides exhibit a distinct relaxation mechanism at the high end of the frequency range.