Type of Document	Dissertation
Author	Ginn, Brent Taylor
URN	etd-08032005-153215
Title	Spatio-Temporal Self-Organization in Micro-Patterned Reactor Arrays
Degree	Doctor of Philosophy
Department	Chemistry and Biochemistry, Department of
Advisory Committee	Advisor Name Title Oliver Steinbock Committee Chair Sanford Safron Committee Member
Keywords	Microfluidic Reaction-Diffusion Microemulsion Belousov-Zhabotinsky
Date of Defense	2005-07-26
Availability	unrestricted
Abstract This dissertation describes experimental methodologies and their application for the study of chemical self-organization in micropatterned reaction systems. The general approach is based on office-printer-assisted soft lithography and allows the fabrication of centimeter-scale devices with reactor units as small as 50 micrometers. For the first projects, the devices are made from the elastomeric material poly(dimethylsiloxane) (PDMS) and are filled with a modified Belousov-Zhabotinsky solution. This excitable reaction-diffusion medium employs 1,4-cyclohexanedione as a bubble-free organic substrate and ferroin or Fe[batho(SO3)2]3 as a redox catalyst/indicator. In PDMS reactors chemical wave propagation is affected by the loss of bromine from the aqueous phase into the elastomer matrix. The strength of this activating process depends on the local surface-to-volume ratio and can increase the wave velocity by a factor of two. For devices with grid-like reactor networks, a pronounced deformation of target patterns and the pinning of spiral waves to single elastomer obstacles as well as to obstacle clusters are observed. Vortex pinning is of particular interest if the spiral tips describe large circular or meandering trajectories. Meandering spiral tips in homogeneous reaction-diffusion systems are characterized by two generically incommensurate radii and frequencies. Micro-patterned reactors are used to create periodic perturbations in space to induce a transition to commensurate radii and frequencies that exhibit a "devil's staircase". The plateaus of the staircase correspond to pinned or complex periodic orbits of the spiral tip. The dynamics are observed at low concentrations of the reactants and display a long induction period of 4-6 hours. Also associated with the waves are long wavelengths and periods. For large trajectories that cover an area greater than 5 mm2, rotational periods are exceedingly long compared to the reaction lifetime, thus making it impossible to observe closed trajectories or repeating sequences. Another interesting application of micro-patterned reactors is the investigation of pinned multi-armed spiral waves to non-excitable obstacles. With increasing obstacle size, the individual arms switch from a repulsive to an attractive state. This transition yields densely aggregated spiral arms and is caused by anomalous dispersion. A kinematic model reproduces the measurements quantitatively and identifies the transition as a supercritical pitchfork bifurcation. More importantly, the method allows for the governing dispersion relation to be measured from spiral waves with a stationary velocity. A new methodology for producing micro-patterned reaction devices from polyester resin is developed to overcome potential problems arising from the loss of bromine into the reactor material. These devices are also suitable for studying a water-in-oil Belousov-Zhabotinsky microemulsion. Kinetic and spectroscopic studies of the polymer show no absorption of octane and bromine, in contrast to poly(dimethylsiloxane). Moreover, studies of spatial constraints on pattern formation reveal interesting characteristics which are investigated further with numerical simulations. Lastly, an experimental approach for studying three-dimensional wave structures is devised and implemented. The approach allows for a series of two-dimensional intensity profiles to be "transformed" into a three-dimensional profile and visualized as an isosurface. This work opens the door for future studies of spatio-temporal self-organization in three dimensions.
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