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Thermodiffusion anisotropy under a magnetic field in ionic liquid-based ferrofluids.
T Fiuza1, M Sarkar2, J C Riedl2
1Sorbonne Université, CNRS, Lab. PHENIX, 4 Place Jussieu, F-75005 Paris, France. regine.perzynski@sorbonne-universite.fr and Grupo de Fluidos Complexos, Inst. de Fisíca, Univ. de Brasília, Brasília (DF), Brazil.
Soft Matter
|May 5, 2021
Summary
Maghemite (γ-Fe2O3) ferrofluids in ionic liquids migrate to colder regions, regardless of temperature or magnetic field. Their thermodiffusion anisotropy diminishes with increased temperature and thermal motion.
Area of Science:
- Materials Science
- Nanotechnology
- Physical Chemistry
Background:
- Ferrofluids composed of maghemite nanoparticles (NPs) in ionic liquids offer unique magnetic and thermal properties.
- Understanding NP behavior in these complex fluids is crucial for advanced applications.
Purpose of the Study:
- To investigate the thermodiffusion behavior of maghemite ferrofluids under varying magnetic fields and temperatures.
- To model and explain the observed anisotropic diffusion and thermodiffusion.
Main Methods:
- Small-angle X-ray and neutron scattering (SAXS/SANS) to characterize interparticle interactions.
- Forced Rayleigh scattering (FRS) to measure mass diffusion coefficients.
- Application of an external magnetic field (H) and temperature gradients (T).
Main Results:
- Maghemite NPs consistently migrated towards colder regions, independent of H and T.
- Anisotropic mass diffusion (Dm) and Soret coefficients (ST) were observed and accurately modeled.
- The anisotropy originated from magnetic dipolar interactions causing concentration inhomogeneities along the field.
Conclusions:
- The thermodiffusion anisotropy in maghemite ferrofluids is primarily driven by magnetic interparticle forces.
- Increased temperature and thermal motion reduce the anisotropy by mitigating magnetic dipolar effects.
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