Rheology, simply stated as the study of the flow and deformation of matter, is afield with grand importance yet a meager following. Be it velocity distributions and
turbulence within the Sun or the flow of jelly from your donut’s center, the field of
rheology offers tools to understanding the simple to the complex. For example, one
such simple experiment that hides far more complex dynamics is the flow of a low
viscosity fluid through a much higher viscosity liquid. This is also known as coring
flow and has been studied extensively for the macro-scale. The dynamics for coring
flow have not been studied, to the best of the author's knowledge, on the micro-scale
and it is that disparity the research detailed here addresses.
There are many important aspects to consider before performing multiphase
micro-fluidic research including what micro-fabrication methods are used, how the
microchip is interfaced to the macro-world, how the fluids will behave, and how the
micro-channel geometry will affect the dynamics. This dissertation addresses those
topics as they apply to the research performed and detailed here. Three different
fabrication techniques are explained, detailed, and used to highlight the benefits and
drawbacks of working on the micro-scale. Bonding is also an important part of
fabrication and so two different methods are discussed. Finally, the way a microchip is
interfaced to the macro-world affects the correlations that can be made. Three different
interfacing systems that worked well are presented.
The fundamental process of coring on the micro-scale is investigated and
explained for circular, square, and rectangular geometries. The simple case of a
Newtonian coating fluid was researched first, followed by the case of a viscoelastic
coating fluid, and finally the case where the coring fluid contained a surfactant. It was
found that, in general, micro-scale coring matches that of the macro-scale except for the
case of a viscoelastic coating fluid. New bubble behavior was observed for high flow
rates through a viscoelastic coating fluid.
As engineers, we wrestle something practical out of our understanding of the
fundamental. This principle was the driving motivation behind the three practical
applications of micro-scale coring flow that were. Coring flow was used to add a
functional coating to capillaries for use in Capillary Electrophoresis, to coat a static
mixer, and to create nozzle-like structures in a micro-channel. The final goal of these
practical applications was to develop a toolbox of procedures and data that can be used
in a wide array of fields including (a) coatings to reduce non-specific binding in
drug/gene delivery applications, (b) coatings for separation and detection techniques
like Capillary Electrophoresis, and (c) a simple means to smoothing rough channels
made via micro-/nano-machining.