Thermoelectricity and thermodiffusion in charged colloids

Abstract

The Seebeck and Soret coefficients of ionically stabilized suspension of maghemite nanoparticles in dimethyl sulfoxide are experimentally studied as a function of nanoparticle volume fraction. In the presence of a temperature gradient, the charged colloidal nanoparticles experience both thermal drift due to their interactions with the solvent and electric forces proportional to the internal thermoelectric field. The resulting thermodiffusion of nanoparticles is observed through forced Rayleigh scattering measurements, while the thermoelectric field is accessed through voltage measurements in a thermocell. Both techniques provide independent estimates of nanoparticle's entropy of transfer as high as 82 meV K(-1). Such a property may be used to improve the thermoelectric coefficients in liquid thermocells.

Colloidal dispersions of oxide nanoparticles in ionic liquids: elucidating the key parameters

“…6 The addition of charged nanoparticles, for example, can improve the thermoelectric properties compared to the use of a solvent alone. 7,8 Increasing the electrical conductivity of colloidal dispersions provides new possibilities, for example, complex electrolytes for electrochemical devices. 6 In the past, several approaches were used to stabilise nanoparticles in ionic liquids.…”

Can charged colloidal particles increase the thermoelectric energy conversion efficiency?

“…Ŝ 0 of the nanoparticles, determined from the best fit of the experimental data, ¶ is 14 meV K À1 for FF-TBuA, slightly smaller in magnitude than that found in our previous study using DMSO-based ferrofluids (see ref. 27 and ESI 2 †). However, this value must be considered with caution due to a large experimental uncertainty in the measured values of electrical conductivity which were measured only at low NP concentrations.…”

“…27 for more in-depth development). The ionic strength and consequently, the activity coefficient of the redox reaction potential is modified due to the inclusion of charged magnetic nanoparticles.…”

“…More specifically, we examine two aqueous ferrofluids made of identical citrate-coated maghemite nanoparticles that are ionically stabilized with either TBuA + (hereafter referred to as FF-TBuA) or Li + (FF-Li) counterions. § As in our previous study, 27 S e is measured as a function of magnetic nanoparticle concentration. We demonstrate that with appropriate control over concerned physical parameters, one can indeed increase the thermoelectric power of the thermocell.…”

“…Ferrofluids (suspension of magnetic nanoparticles in non-magnetic liquid media) present high Soret coefficients 25,26 as well as an additional control parameter because of their magnetic nature and are thus considered to be promising candidates for such investigations. We have recently reported the combined experimental study on the thermodiffusion and Seebeck coefficient in ferrofluids 27 where both Soret and Seebeck coefficients were measured as a function of nanoparticle (NP) concentration. While the resulting thermoelectric power was found to decrease by the inclusion of magnetic nanoparticles in a DMSO (dimethyl sulfoxide) based ferrofluid, our work has served as a proof-of-principle demonstrating the contribution of thermodiffusion of charged colloidal particles to the total thermoelectric voltage of the carrier fluid.…”