Dielectric spectroscopy of nanofluids in deionized water: Method of removing electrode polarization effect

Abstract

HypothesisThe electrode polarization observed in the measured complex dielectric frequency responses of the nanosuspensions could be isolated by using time-domain analysis. ExperimentsComplex impedance and dielectric frequency responses of various ferroelectric and magnetic nanofluids were ultrasonically dispersed in deionized water and measured within 20 Hz to 6 GHz range for the first time. A general Kramer-Krönig continuous relaxation model was fitted to the dielectric spectra in the least-squares sense using the Tikhonov’s regularization. The independent ζ-potential measurements of the BTO-C2 and Fe3O4 nanosuspensions were performed. FindingsThree distinct peaks were observed in the time-domain responses. Zero padding of the two slowest peaks, followed by the inversion of the corrected time domain responses, resulted in the flattening of the lower frequency portion of the dielectric constant. The effective medium theory model coupled with the pattern search optimization routine, were used to match these flattened responses. The surface charge on the nanoparticles was estimated from the measured ζ-potential using the Gouy-Chapman-Stern-Grahame model. The resulting values were comparable with the ones obtained from the effective medium theory fitting procedure, which proves effectiveness of the proposed approach at removing the electrode polarization effects. The proposed method has the advantage over the existing ones, because it is carried out in time domain and requires no prior knowledge about the underlying relaxation time amplitude distributions or specific equivalent circuits.