Experimental research of surfaced nanoparticle thermal transport in a porous medium

Experimental research on thermally induced nanocolloid transport in a porous environment is presented. Addition of excess surfactant to a colloid with dispersed phase made of surfaced nanoparticles results in a decrease of effective Soret coefficient in a porous environment. It is shown that with sufficient amounts of surfactant added, this effect extends to a reversal of nanoparticle thermophoretic transport direction, and that the effect shows a tendency of saturation. A mechanism of thermal transport that involves slip velocity of surfactant molecules appearing near pore walls is evaluated as a possible cause of the decrease of Soret coefficient. Effects of temperature on particle thermophoresis are analyzed, revealing a decrease of Soret coefficient with the increase of temperature. In order to better understand surfactant motion in the porous environment, a series of experiments characterizing thermoosmotic motion of a mixture of surfactant diluted in pure carrier fluid through a porous layer is performed.