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Sadden, Joseph Lee Mohamed

University of British Columbia

Localizing particles as they flow through micro-fluidic devices is a direct pathway to improving the usefulness of such devices. A key demonstration of this is found in droplet-on-demand bio-printing, where the ability to dispense a particle depends sensitively on where within the nozzle the particle is. If particles can be preferentially localized in the ejection region of the nozzle, the likelihood of empty droplets is reduced and throughput of the device increases. This work focuses on the development of a micro-fluidic platform to migrate micro-scale particles as they flow through a channel, highlighting the engineering considerations of the platform. Placing this device upstream of a dispensing nozzle and tuning the flow focusing parameters can increase the likelihood of a particle being dispensed. Beginning with an introduction into the available methods of particle focusing, this work then compares the methods to justify the use of viscoelastic effects. Understanding the focusing mechanism clarifies the requirements and constraints of the platform. These involve imaging of the flows, characterization of the device, and the interplay between flow and focusing parameters. The platform provides steady, laminar, unidirectional flows for flow-rates over approximately three orders of magnitude. The platform is characterized by assuming Poiseuille flow and measuring the flow field at the mid-plane using Bright-Field Particle Image Velocimetry. Once characterized, the ability to migrate micro-particles was tested. Using multiple channel geometries and process fluids, the distribution of particles across the channel was extracted using computer vision. These distributions were compared between Newtonian and viscoelastic fluids to demonstrate the effect of introducing an elastic polymer into the fluid. The flow focusing was then compared against a simplified model of the elasticity-induced particle migration. The platform is able to provide partial focusing, with no major differences between the process fluids used, across three channel geometries. Tapered channels provide slightly better focusing than straight channels of equal length, although they also demonstrate more significant inertial focusing effects. Single-line focusing was not achieved in any of the steady flow experiments. The preliminary oscillatory flow focusing performed is able to produce single-line focusing in straight circular channels at Re < 1.

Text; Still Image; Dataset

2024-09-12

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/89225

Electrical and Computer Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/