Nanoparticle dispersion in disordered porous media with and without polymer additives.

In purely viscous Newtonian fluids, mechanical mixing of the fluid stream as it moves through an unstructured porous medium controls the long-time dispersion of molecular tracers. In applications ranging from environmental remediation to materials processing, however, particles are transported through porous media in polymer solutions and melts, for which the fluid properties depend on the shear rate and extent of deformation. How the flow characteristics of polymer solutions affect the spreading of finite-sized particles remains poorly understood - both on the microscopic scale as local velocity profiles, and on the macroscale as dispersion. Here, we show across a range of flow rates and disordered porous media configurations that the long-time transport coefficients of particles flowed in water, in a viscous Newtonian fluid, and in a non-Newtonian shear-thinning polymer solution collapse onto scaling curves, independent of the fluid rheology. Thus the addition of polymer does not impact nanoparticle dispersion through disordered porous media.