Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Physics

Supervisor

de Bruyn, John R.

2nd Supervisor

Poepping, Tamie L.

Joint Supervisor

Abstract

A yield-stress fluid is a material that has properties of both solids and conventional liquids that only begins to flow when subject to a finite stress. The behaviour of yield-stress fluids is interesting and important in many applications. It is expected that the rheological properties of a yield-stress fluid will change when confined to a region with a length scale comparable to the characteristic scale of its microstructure. The particle size and polydispersity of two yield-stress fluids, Carbopol and poly(N-isopropylacrylamide), were determined using dynamic light scattering. A rheological characterization was performed on these two yield-stress fluids. Flow of water in 1 cm long square microchannels ranging in width from 100 to 500 micrometers was simulated. Microchannels were fabricated using a soft lithography method and used in micro-particle image velocimetry experiments to visualize the confined flow of water, Carbopol, and poly(N-isopropylacrylamide). The flow of Carbopol and poly(N-isopropylacrylamide) was calculated using an equation for laminar flow of a Herschel-Bulkley fluid in a circular pipe. This analysis procedure showed that Carbopol experiences a significant increase in yield stress when confined to microchannels less than 200 micrometers in width. Time limitations prevented us from fully characterizing the confinement effects in these materials. Nonetheless the required experimental techniques and data analysis procedures have been substantially improved over previous work, paving the way for future research in this area.

Summary for Lay Audience

A yield-stress fluid is a material that has properties of both solids and conventional liquids that only begins to flow when subjected to a finite stress. It is expected that the properties of these yield-stress fluids with change when confined to a region on the order of its particle size. The particle size of two yield-stress fluids, Carbopol and poly(N-isopropylacrylamide), were determined. The flow properties of these fluids were characterized. Microchannels were fabricated and used in flow visualization experiments. Time prevented a full characterization of the confinement effects in these materials. Nonetheless the required experimental techniques and data analysis procedures have been substantially improved over previous work, paving the way for future research in this area.

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