Fabrication of polymer particles as model colloids in soft matter filtration

With the energy-efficient and reliable removal of particles, bacteria, cells, cell debris and other micron-sized impurities, micro- and ultrafiltration have leveraged as wide-spread separation technologies across industries ranging from water treatment and food processing to biotechnology and pharmaceuticals. However, their applications are hampered by a severe flux decline caused by retained colloids accumulating in front of the membrane, building up a filter cake and adding an additional hydraulic resistance to the overall filtration process, yielding the separation process inefficient. Most models describing the filtration processes ground on empirical models for specific separation tasks at certain operation conditions. However, a general mechanistic model describing a broad range of filtration conditions for the retention of colloids with various properties based on particle interaction potentials and colloidal properties is yet to be developed. Cornerstone of such mechanistic models is the observation of isolated phenomena during filtration in idealized environments with well-defined process conditions. The present thesis provides two experimental approaches for filtration investigations in simplified environments on different size scales, starting with microfluidic investigations of particle properties on the hydraulic resistance of a filter cake by precisely controlling particle softness, shape, porosity, quantity and dispersity. Despite the precise adjustment of specific filtration parameters, the transferability of the results in the idealized environment to real-world filtration is challenged. Therefore, a continuous volumetric 3D printing approach is presented for upscaling particle production at high resolution, which could potentially be applied in larger filtration experiments and less idealized environment but at maintained precise filtration conditions. The second experimental approach features the filtration of microgels as model foulants in a lab-scale filtration cell with a microfiltration membrane at more realistic filtration conditions, where foulant degradation causes unexpected flux declines during the initiation phase of filtration. Based on the observation of foulant degradation, an in-situ method for determining elastic hydrogel properties and coupled with CFD-DEM simulations, visualization of force distribution inside hydrogel polymer networks is proposed to precisely determine and tune the rigidity of hydrogels for filtration studies. Further functionalization of the polymer network by integrating force probes is envisioned to emphasize force distribution inside soft matter filter cakes. Building on these insights, this thesis enhances the understanding of soft matter filtration and contributes to a mechanistically-grounded fouling model applicable for various filtration processes. The discussion extends to improve filtration-mimicking experiments, leveraging state-of-the-art 3D printing technologies and polymer functionalization to close the gap between lab-scale filtration and real-world applications.