This thesis investigates the transport and sorting of capsules (elastic membranes enclosing a liquid core) using viscous flow in complex vessel geometries. Of particular interest is passive sorting by deformability using only the fluid-structure interaction between the capsule, the viscous fluid and the geometry of the vessel. Millimetric alginate-ovalbumin capsules in the regime of negligible fluid inertia are used in this work. In order to characterise the elastic properties of the capsules, a novel numerical finite element model of the compression of a thick-shelled capsule between parallel plates is implemented. The constitutive model of the capsule membranes was determined by comparison to experimental data: a Yeoh constitutive model with the ratio of constants $C_1 = 1$, $C_2 = 0$ and $C_3 = 10$ describes the capsules used. Three geometries are investigated in this work. (i) A T-Junction bifurcation. Capsule deformation in the T-Junction bifurcation is characterised by the maximal length of the capsule $L_{max}$ and depends on the ratio of viscous to elastic forces, the capillary number $Ca$. The maximal length, $L_{max}$, is especially sensitive at distinguishing soft capsules by their deformability. The sensitivity of $L_{max}$ to capsule compliance and the large deformations that can be achieved makes the T-junction a promising geometry in which to measure elastic properties of the capsules. The rate of relaxation of the capsules after the bifurcation is independent of their deformation. (ii) A half-cylinder obstacle in a channel followed by a sudden expansion. We show that the half-cylinder obstacle causes capsule trajectories to vary depending on deformability. Capsules with a factor of three difference in deformability can be separated. A practical feature of the system is its relative insensitivity to the initial lateral position of the capsules in the channel. However, while the results are reproducible across different capsules, the variations in final position amount to 10 \% at fixed parameters. As these experiments were conducted with the same capsule under identical flow conditions, this is likely to represent the best case scenario. (iii) We adapt the pinched flow fractionation (PFF) geometry to the sorting of capsules. We show that the standard PFF device cannot be used to sort capsules. However, a novel mode of operation, termed the ``T-Junction'' mode, shows great promise for the sorting of capsules. The PFF device in the T-Junction mode separates capsules with a factor of 1.5 difference in deformability. This is twice as sensitive as the half-cylinder device, although larger variability was observed in the PFF device.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:728032 |
| Date | January 2017 |
| Creators | Haener, Edgar |
| Contributors | Juel, Anne ; Heil, Matthias |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/microfluidic-segregation-of-capsules(a7e001f1-536c-475d-83d5-82aaa4098f5b).html |
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