0000000000201689
AUTHOR
Guillaume Mériguet
The cage elasticity and under-field structure of concentrated magnetic colloids probed by small angle X-ray scattering
International audience; In the present study we probe the bulk modulus and the structure of concentrated magnetic fluids by small angle X-ray scattering. The electrostatically stabilized nanoparticles experience a repulsive interparticle potential modulated by dipolar magnetic interactions. On the interparticle distance length scale, we show that nanoparticles are trapped under-field in oblate cages formed by their first neighbours. We propose a theoretical model of magnetostriction for the field-induced deformation of the cage. This model captures the anisotropic features of the experimentally observed scattering pattern on the local scale in these strongly interacting colloidal dispersions
Relaxation of the field-induced structural anisotropy in a rotating magnetic fluid
The relaxation of field-induced anisotropy in a magnetic fluid with dominant repulsion is theoretically modeled and experimentally measured by small angle neutron scattering on a sample rotating at angular velocity ω. The scattered pattern distortion scales as the Mason number Mn=ω·τq, τq being the q-dependent diffusion time of nanoparticles. The model accounts for the magnetophoretical drift in the non-homogeneous self-magnetic field of the assembly, continuously created by the thermal noise. The Mn-dependence of the pattern distortion is well described without any adjustable parameter.
Thermodiffusion anisotropy under a magnetic field in ionic liquid-based ferrofluids
International audience; 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 to be repulsive by small angle scattering of X-rays and of neutrons, with a second virial coefficient A2 = 7.3. A moderately concentrated sample at Φ = 5.95 vol% is probed by forced Rayleigh scattering under an applied magnetic field (up to H = 100 kA m-1) from room temperature up to T = 460 K. Irrespective of the values of H and T, the NPs in this study are always found to migrate towards the cold region. The in-field anisotropy of the mass diffusion c…