Investigation of dielectrophoretic effects in porous structures
The recovery of submicron particles, especially nanoparticles, is becoming more and more attractive. Various approaches for separating, recovering, and redispersing nanoparticles, such as ultracentrifugation, solvent evaporation, the addition of antisolvent carbon dioxide, and temperature control are being actively investigated. However, all of the technologies mentioned above are top-down methods and batch wise processes with high energy consumption and cost. The conventional method often used in industry is membrane filtration, which could separate nanoparticles continuously due to size exclusion or interception. Fouling in membrane filtration systems is, however, inevitable. Nanoparticles on the membrane surface and in the pores may significantly and rapidly reduce the permeate flux, and may even block the membrane completely. Dielectrophoresis (DEP), an effect of particle motion due to dielectric polarization in inhomogeneous electric fields, is believed to be a very promising bottom-up technology with proved capability of highly selective nanoparticle manipulation. The DEP force is proportional to the particle's volume and is driven by the electric field gradient. As a result, the manipulation of nanoparticles requires vast electric field gradients, which could either be generated by employing technically mature (and small) electrode configurations together with a high voltage input or by manipulating homogeneous electric fields using material interfaces. The polarization of a stationary porous dielectric due to an applied electric field will cause a highly inhomogeneous electric field inside of the pores, which is very suitable for trapping nanoparticles. Experiments using model porous media have shown that the distribution and intensity of the resulting gradient and thus the capability to retain particles is greatly dependent on the shape of the pores and the material of the porous structure. We could show that an application of DEP in the separation and resuspension of particles in the nm-range using macroporous filter is possible. We are further able to simulate and experimentally validate the separation of such particles in a packed-bed of glass spheres. Aim of this project is to understand the dependence of the dielectrophoretic particle retention in a filtration process on dielectric properties and pore geometries of ceramic foams. Further, the interplay between energy input and process efficiency shall be highlighted and explained. This work shall be supported using numerical simulations in combination with state-of-the-art in- and ex-situ imaging techniques (X-Ray microtomography and MRI) to further investigate the detailed trapping mechanism and trapping positions of the particles inside the foam.