Thermodiffusion anisotropy under a magnetic field in ionic liquid-based ferrofluids

Abstract

Ferrofluids based on maghemite nanoparticles (NPs), typically 10 nm in diameter, are dispersed in an ionic liquid (1-ethyl 3-methylimidazolium bistriflimide - EMIM-TFSI). The average interparticle interaction is found repulsive by...

Ion specific tuning of nanoparticle dispersion in an ionic liquid: a structural, thermoelectric and thermo-diffusive investigation

“…61 Note that here, a weak decrease of the short range ordering could be compensated by the weak decrease of dipolar magnetic interaction (attractive on average in zero field). 29 In summary, it then seems reasonable to extend our conclusion and assume that the compressibility w and the second virial coefficient A 2 are to the first order, both temperature-independent, for dispersions at any volume fraction for the three counter-ions within the experimental temperature range explored.…”

“…61 Note that here, a weak decrease of the short range ordering could be compensated by the weak decrease of dipolar magnetic interaction (attractive on average in zero field). 29…”

“…26 It is this ionic self-organisation around the charged NPs which is usually put forward as being responsible in RTIL for producing the repulsion necessary to counterbalance the van der Waals interparticle attraction (and the magnetic dipolar interaction ifas is the case here -the NPs bear a magnetic moment). This selforganisation can come either from an alternating ionic layering around the NPs 13,19,20,[27][28][29] and/or from solvation forces, associated with hydrogen bonding. 15,30 The chosen system is made of magnetic and charged maghemite nanoparticles in EAN.…”

Effect of an excess of surfactant on thermophoresis, mass diffusion and viscosity in an oily surfactant-stabilized ferrofluid

“…A marked decrease of ŜNP /kT with the temperature increase is also observed here, at 85 • C, ŜNP /kT is of the order of + 0.2 K −1 , irrespectively to OA added concentration. In literature, very few experimental colloidal systems present both S T > 0 and ∂S T /∂T < 0, we can quote the work by Fiuza et al [66] on ferrofluids dispersed in an Ionic Liquid and the work by Sehnen et al [8] on aqueous ferrofluids with two different added salts. While S T is frequently negative in aqueous ferrofluids, see for example [9], in this latter study, S T is positive with ∂S T /∂T < 0 with added TBAOH salt.…”

Ferrofluids and bio-ferrofluids: looking back and stepping forward

“…The electrostatic stabilization mechanism was extended to a non-aqueous highly polar solvent dimethyl sulfoxide (DMSO) 125 and also to various ionic liquids. [126][127][128][129] DMSO and ionic liquids have a permittivity lower than that of water, and consequently the stabilization of magnetic nanoparticles by electrostatic repulsion is expected to be more difficult than in water. Long term (several years) colloidal stability, even at relatively high temperatures (up to 200 °C), was achieved recently by adapting the interfacial properties of magnetic nanoparticles to pure ionic liquid carriers.…”