Date of Award

Summer 2021

Publication Type

Thesis

Degree Name

M.A.Sc.

Department

Mechanical, Automotive, and Materials Engineering

Keywords

Capacitive based sensor, Capillary number, Droplet regulation, Lab-on-a-chip, Pneumatic chamber, T-junction droplet generator, Microfluidics, Precision droplet generators

Supervisor

D. Ting

Supervisor

J. Ahmed

Rights

info:eu-repo/semantics/openAccess

Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

Abstract

Microfluidic droplet generation is popular in lab-on-a-chip based biochemical analysis because it can provide precise and high throughput fluids in the form of small droplets. This thesis presents a T-junction microdroplet generator with pneumatic actuation for regulating droplet size and a capacitance-based sensor with real-time sensing capability for characterizing droplet composition and size. The multi-layer device developed in this thesis is compatible with rapid manufacturing using a desktop-based laser cutter to fabricate the fluidic and pneumatic layers. A finite element based numerical model was developed to predict the best operating and geometric parameters for droplet generation. It was revealed that the model could generate monodisperse droplets with a capillary number of 0.0007 for an aspect ratio of 1.11:1 and that the electrode width to droplet size ratio of 1:0.95 was the best size for sensing droplet movement. The results with pneumatic control showed working pneumatic pressure of up to 0.4 MPa is achievable, resulting in a 38% reduction in droplet size compared to a reference droplet. The continuous fluid used in the model was 0.1 ml/min, whereas the conventional method was 0.19 ml/min, resulting in a 38 percent reduction in droplet size. The droplet size decreased by 9.7 percent as the pressure inside the pneumatic chamber is increased by 0.1 MPa. As a result of this reduction, the capacitance value sensed decreases by 4.7 percent when a droplet (dispersed material) is fully positioned between electrodes, whereas it increases by 2.0 percent when only continuous fluid is present. Similarly, in material characterization, when the dispersed material was changed, the variation in capacitance for a droplet movement was observed to change. The multi-layer droplet generation, with simple and simultaneous sensing as well as regulation capability presented in this thesis, can be useful for the development of precision droplet generators with closed-loop control.

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