Effect of TiO2 nanoparticles on the ion mobilities in transformer oil-based nanofluid

TiO2 nanoparticles with an average diameter of 6 nm were synthesized and well dispersed in transformer oil to prepare nanofluids (NFs). Influence of nanoparticles on the ion migration property of NFs was investigated via reversal polarity method under different applied electric fields and temperatures. It was found that the ion mobility in TiO2 nanofluid is increased to 4 times of that in pure oil (PO) under the electric field of 5 kV/m, and then decreased abruptly and keeps around one tenth of ion mobility in PO from 50 to 150 kV/m. While the case in PO keeps almost constant throughout the applied fields. The results of the conductivity and ion characteristics of PO and NFs reveal that the presence of nanoparticles can reduce the diameter of impurity ions by shrinking hydrated solvated shell and greatly enhance their mobility at low electric fields. With the increasing of electric stress, the charged nanoparticles become the major conduction contributor and drift slowly due to the higher viscous resistance from oil molecules.