8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P9.74Tue 611:23-14:00Drift velocity and driving forces in inhomogeneoussuspensionsMingcheng Yang 1 and Marisol Ripoll 11 Forschungszentrum Jülich, Leo-Brandt-Straße, 52425, Jülich, GermanyDrift velocity and mechanical driving force are not directly proportional in the case of inhomogeneoussuspensions, where a space dependent mobility induces an extra contribution to the driftvelocity. This phenomenon is of particular relevance, for example, for the experimental techniquesknown as NFM (non-equilibrium measurements), which quantify the force suffered by a suspendedparticle from its trajectories. For systems in confinement, the proximity to a wall produces a diffusioncoefficient dependent on the distance to the wall, what translates into an extra contributionto the drift velocity even in the absence of driving forces. Systems in temperature gradients displaya phoretic velocity that is not necessary directly proportional to the so-called thermodiffusioncoefficient, albeit this is widely accepted. Different driving forces on a mixture are induced by atemperature gradient what translates into the component segregation. We show that these drivingforces constitute the physical picture behind the thermodiffusion effect, and provide an alternativeexpression of the Soret coefficient which can be applied to both colloidal suspensions andmolecular mixtures. By means of computer simulations with a temperature gradient, we providequantitative support to this theoretical framework in a non-equilibrium system. Furthermore, bycombining the validated expression with a hydrodynamic argument, we can qualitatively explainthe intricate size dependence of the thermodiffusion in dilute polymer solutions.74