Thermodiffusion of magnetite nanoparticles in ferrofluid-doped micellar systems and in ferrofluids investigated by using the single-beam Z-scan technique

The Z-scan experimental technique is used to measure the concentration-dependent Soret coefficient of surfacted magnetic nanoparticles in water [pure ferrofluid (FF)l 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-T(FL) similar or equal to 0.4 x D-T(FF). The Soret effective mobilities evaluated are mu(FF)(s)similar to 6x10(11) s kg(-1) and mu(FL)(s) similar to 2 X 10(11) s kg(-1) for the pure ferrofluid and micellar media, respectively. From a nanoscopic point of view, the smaller value of mu(FL)(s) when compared to mu(FF)(s) 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. (c) 2006 Optical Society of America