Multidimensional fractionation of ultrafine particles in microsystems

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For the production of comparatively high-priced products in various industries, e.g. active pharmaceutical ingredients, ceramics and printable nanoparticle inks, the requirements for particle properties are constantly increasing, with particles in the size range below 10 µm with defined properties increasingly required. Impurities, such as those caused by wear during comminution processes, must also be removed. The necessary multidimensional fractionation of technical suspensions with particles below 10 µm is, however, not satisfactorily possible with state-of-the-art separation methods. Therefore, a microsystem of combined passive and active microelements for multidimensional fractionation with respect to the particle properties size and electrical permittivity shall be developed and investigated in this project. The systems are manufactured by the Institute of Microtechnology using the FLICE process (Femtosecond Laser Irradiation and Chemical Etching) in glass and dry etching (Deep Reactive Ion Etching) in silicon. In the first funding phase, microelements have been developed based on two different principles: the passive Deterministic Lateral Displacement Method (DLD) and (di)electrophoretic forces in (inhomogeneous) electric fields. In the second funding phase, the focus is on integrating the methods into one microsystem. By superposition of the DLD with (inhomogeneous) electric fields, a combined separation according to size and charge or permittivity shall take place. Intensive µPIV investigations as well as coupled CFD-DEM simulations are at the core of the understanding of the multidimensional separation. The influence of the flow velocity and the post shape on the separation result has been investigated so far. The work will be continued in the following, especially with regard to multidimensional separation. The overriding goal of the work, in particular also of the simulations, is the targeted design and layout of the structures with regard to the multidimensional classification of technical suspensions with the highest possible solids content and the highest possible throughput. Together, the two project partners use the findings to produce advanced microelements and combine them into an effective overall system. Due to the wide particle size distribution of real suspensions and the danger of clogging, a further fractionation step has to be integrated on the microchip in order to separate the upper particle size range. Based upon the experimental and simulative results and a deeper understanding of the working principles, models and guidelines for the design of microsystems for technical use are to be developed.