Microfluidic model systems used to emulate processes occurring during soft particle filtration

Abstract

Cake layer formation in membrane processes is an inevitable phenomenon. For hard particles, especially cake porosity and thickness determine the membrane flux, but when the particles forming the cake are soft, the variables one has to take into account in the prediction of cake behavior increase considerably. In this work we investigate the behavior of soft polyacrylamide microgels in microfluidic model membranes through optical microscopy for in situ observation both under regular flow and under enhanced gravity conditions. Particles larger than the pore are able to pass through deformation and deswelling. We find that membrane clogging time and cake formation is not dependent on the applied pressure but rather on particle and membrane pore properties. Furthermore, we found that particle deposits subjected to low pressures and low g forces deform in a totally reversible fashion. Particle deposits subjected to higher pressures only deform reversibly if they can re-swell due to capillary forces, otherwise irreversible compression is observed. For membrane processes this implies that when using deformable particles, the pore size is not a good indicator for membrane performance, and cake formation can have much more severe consequences compared to hard particles due to the sometimes-irreversible nature of soft particle compression.

Conformational changes influence clogging behavior of micrometer-sized microgels in idealized multiple constrictions

“…The channels of the microfluidic devices used in this work have a variety of entrance angles. In previous work 23 , we found that the entrance angles do not have an influence on overall clogging behavior of micrometer-sized particles that are smaller than the pore. Here we investigate larger particles in detail.…”

“…Microgels were synthesized and characterized as described in previous work 23 . Polyacrylamide (pAAm) microgels are used as model particles for the channel clogging experiments.…”

“…Microfluidic experiments were performed as described in previous work 23 . The microfluidic devices we use to simulate membrane filtration are composed of a main channel with an inlet and an outlet.…”

“…Image analysis was performed as described in previous work 23 . Self-written matlab scripts are used to analyze the images; for the clogging experiments, we determine the average clog constriction position, so how deep each channel clogs.…”

Templating the morphology of soft microgel assemblies using a nanolithographic 3D-printed membrane

“…However, the filtration of soft particles is more complex. Soft particles can undergo deformation, interpenetration, and compression 5 , such that the resulting filter cakes deform partly reversibly and irreversibly during filtration 6 . Additionally, the particles in a soft cake can rearrange their position due to deformation and often create crystalline cake regions, such that the cake becomes strongly non-isotropic 7 – 9 .…”