Thermal diffusion and Soret feedback of gold-doped polyorganosiloxane nanospheres in toluene

We have investigated diffusion and thermal diffusion properties of light-ab sorbing colloidal polyorganosiloxane microgels containing tiny nanometer-si zed gold clusters dispersed in toluene. Transient holographic gratings allo w for very subtle perturbations in the linear regime where Soret feedback i s negligible. Gold-doped colloids of different size and crosslink ratios sh ow different Soret coefficients but identical thermal diffusion coefficient s D-T Undoped colloids tend to aggregate, but a consistent interpretation i s obtained if an identical D-T is assumed for the doped, the undoped, and t he aggregated particles. Previously reported Soret feedback measurements on similar systems incidentally yielded comparable Soret coefficients. We sho w, however, that they suffer from strong convective perturbations.