The Z-scan experimental technique is used to measure the concentration-dependent Soret coefficient of surfacted magnetic nanoparticles in water [pure ferrofluid (FF)] and in a micellar lyotropic mixture [lyotropic doped with ferrofluid (FL)]. In both cases, the magnetic-particle contribution to the Soret coefficient is shown to be proportional to its concentration. In the case of the ferrofluid-doped lyotropic system, it was possible to evaluate the Soret coefficient associated with the micelles under a temperature gradient. The thermal diffusion coefficients keep the relation D<sup>FL</sup><sub>T</sub> ≃ 0.4 ×D <sup>FF</sup><sub>T</sub>. The Soret effective mobilities evaluated are μ<sup>FF</sup><sub>s</sub> ∼ 6×10<sup>11</sup> s kg<sup>−1</sup> and μ<sup>FL</sup><sub>s</sub> ∼ 2 × 10<sup>11</sup> s kg<sup>−1</sup> for the pure ferrofluid and micellar media, respectively. From a nanoscopic point of view, the smaller value of μ<sup>FL</sup><sub>s</sub> when compared to μ<sup>FF</sup><sub>s</sub> could be pictured as an additional resistance of the micellar medium to the particle's flow imposed by the temperature gradient. This procedure gives a new way of determining the Soret coefficient of a weakly absorbing medium.
© 2006 Optical Society of America
Original Manuscript: April 3, 2006
Revised Manuscript: July 13, 2006
Manuscript Accepted: July 14, 2006
Sarah Alves, Fabio Luiz Sant'Anna Cuppo, Alain Bourdon, and Antonio Martins Figueiredo Neto, "Thermodiffusion of magnetite nanoparticles in ferrofluid-doped micellar systems and in ferrofluids investigated by using the single-beam Z-scan technique," J. Opt. Soc. Am. B 23, 2328-2335 (2006)