(412f) Differentiating Effects of Geometry and Fluid Rheology on the Dispersion of Particles in 2-D Microfluidic Porous Media Via Microfluidic Experiments and Computations

Both fluid crowding and geometric confinement alter the transport of submicron particles through complex media. This scenario appears across a broad range of technological and environmental settings, e.g. when nanoparticles are used to enhance oil recovery from tight formations, to remove toxic compounds from wastewater, or to deliver therapeutic compounds to specific tissues within the human body. Because the efficacy of the particles depends in part on the ability to direct their transport, it is essential to understand how fluid properties and geometry separately affect the dispersion of submicron particles. Here, we show via pore-scale experiments and computational studies how 2-D geometry and fluid viscoelasticity differently affect the dispersion of microscale particles in microfluidic porous media. Experimentally, particles suspended in water/glycerol mixtures and in polymeric solutions of partially hydrolyzed polyacrylamide (HPAM) were flowed through nano- and micropost arrays of varying post arrangements and spacings and their trajectories over time obtained using imaging processing methods. Longitudinal dispersion was not affected by either post geometry or fluid nature. In sharp contrast, the transverse dispersion of particles flowed in the HPAM solution was increased in ordered post arrays but not in randomly distributed post arrays. At the pore scale, the enhanced transverse dispersion originated from the increased likelihood that particles switched between streamlines when flowed in the polymer solution, leading to a broadening of the velocity distributions and an increase in the velocity fluctuations. The experimental results in strong confinement in Newtonian fluids are consistent with simulations. These studies provide the knowledge necessary to predict particle dispersion in varying hard and soft confinement, relevant for a range of engineering applications.