Structural, thermodiffusive and thermoelectric properties of maghemite nanoparticles dispersed in ethylammonium nitrate

Abstract

Ethylammonium nitrate (ionic liquid) based ferrofluids with citrate-coated nanoparticles and Na+ counterions were synthesized for a wide range of nanoparticle (NP) volume fractions (Φ) of up to 16%. Detailed structural analyses on these fluids were performed using magneto-optical birefringence and small angle X-ray scattering (SAXS) methods. Furthermore, the thermophoretic and thermodiffusive properties (Soret coefficient ST and diffusion coefficient Dm) were explored by forced Rayleigh scattering experiments as a function of T and Φ. They were compared to the thermoelectric potential (Seebeck coefficient, Se) properties induced in these fluids. The results were analyzed using a modified theoretical model on ST and Se adapted from an existing model developed for dispersions in more standard polar media which allows the determination of the Eastman entropy of transfer (ŜNP) and the effective charge (Z0e f f) of the nanoparticles.