Diffusion and thermodiffusion studies in ferrofluids with a new two-dimensional forced Rayleigh-scattering technique
Résumé
The authors present a new simple 2-dimensional forced Rayleigh-scattering (FRS) exptl. set-up for detn. of the nanoparticle-diffusion coeff. (DM) and the Soret coeff. (ST) in colloids. For this purpose, the authors give a 2-timescale model for the evolutions of temp. and colloid concn. (similar to that given for a former 1-dimensional FRS method) and a complete description of the signals diffracted by a squared-lattice grating. Both transport properties in ferrofluids (magnetic colloids) detd. with this new set-up are in good agreement with those found with samples already studied using the 1-dimensional technique. This work is completed by studying new samples. Exptl. results the authors obtained confirm and make clearer the following: (i) the strong Soret effect in ferrofluids has a nanoparticle origin and (ii) also, this origin lies in the immediate surroundings of the nanoparticles (ionic or surfacted coating and dispersion liq.).