## Investigation of dielectrophoretic effects in porous structures

The aim of the project is to investigate the influence of structural parameters of porous materials as well as their dielectric properties on particles flow in superposition of inhomogeneous electric fields. The conventional method often used in industry is membrane filtration. However, the use of porous media for the separation of colloids leads to a rapid blocking of the porous structures. In our preliminary work it could be shown that such fouling can be reduced by dielectrophoresis (DEP) significantly. Here, the DEP force is proportional to the particle volume and the voltage square, but inversely proportional to the electrode distance to the power of 3. As a consequence, very high voltages or extremely small electrode distances are required for the separation of small particles. The approach presented in this project seeks to circumvent this dilemma by bringing a porous dielectric into the electric field, which can cause very large field gradients locally. The electric field captures the particles in the filter material and can be easily backwashed later with the electric field turned off. In order to obtain a suitable structure, the influence of porosity parameters and material in the electric field on the separation performance is systematically investigated. The following working hypotheses are checked:

(i) The retention capacity can be influenced by varying the pore structure (model structures, 1st generation, completed).

(ii) The retention capacity can be specifically controlled by the material itself (as a dielectric) (real foam structures, 2nd generation, running).

(iii) Metallic nanoparticles introduced into the solid matrix of the porous materials act as floating electrodes and locally enhance the electric field gradients (hybrid materials, 3rd generation, applied for).

In the third generation, the material dependence is to be investigated by a systematic change in the polarizability and the proportions of the conductive component of the filter (P02/03). This will significantly contribute to the understanding of the whole process. Investigations of DEP filtration using imaging techniques along with CFD simulations on the process will allow a deeper understanding of the process and provides opportunities for optimization. For this purpose, the cooperation with the AG Odenbach (P04/03) for the determination of the three-dimensional structure of real foams as well as with the AG Dreher (P03/03) for the investigation of real flow patterns in the same foam structures will be continued. These results can be used to validate the simulations. This results in a deeper and broader understanding of the DEP process and allows for a targeted formulation of the material structure and its functionalization.

Fig. 1:
a)
Particle deposits on a single
structure

**Publications within MIMEMIMA:**

Pesch, G. R., Lorenz, M., Sachdev, S., Salameh, S., Du, F., Baune, M. Boukany, P. E., Thöming, J. (2018). Bridging the scales in high-throughput dielectrophoretic (bio-)particle separation in porous media, Scientific Reports 8, 10480

Pesch, G. R., Du, F., Baune, M. & Thöming, J. (2017). Influence of geometry and material of insulating posts on particle trapping using positive dielectrophoresis, Journal of Chromatography A 1483, 127-137

Wang Y, Du F, Pesch GR, Köser J, Baune M, Thöming J (2016) Microparticle trajectories in a high-throughput channel for contact-free fractionation by dielectrophoresis, Chemical Engineering Science 153, 34–44

Pesch, G. R., Kiewidt, L., Du, F., Baune, M. and Thöming, J. (2016). Electrodeless Dielectrophoresis: Impact of geometry and material on obstacle polarization. Electrophoresis 37, 291–301

Pesch, GR., Du, F., Schwientek, U., Gehrmeyer, C., Maurer, A., Thoming, J. and Baune, M. (2014) Recovery of submicron particles using high-throughput dielectrophoretically switchable filtration, Separation and Purification Technology, 132, 728-735