Semester

Spring

Date of Graduation

2009

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Chemistry

Committee Chair

Kenneth Showalter.

Abstract

The synthesis, structure and properties of stimuli responsive gels are reviewed. A flow through reactor is constructed by attaching a secondary chamber to the output of a continuously stirred tank reactor (CSTR). The dynamical behavior of the primary and secondary chambers is characterized by carrying out the bromate-sulfite-ferrocyanide reaction in the reactors. The dynamical behavior of the secondary chamber was found to mimic that of the primary chamber. In addition, the secondary chamber offers spatially homogeneous and non-stirred pH oscillations for chemomechanical oscillators and walkers. Chemomechanical oscillators are obtained by placing poly(NIPAAm-co-MAAc) gel rods of diameters less than 530 mum into the secondary chamber of the flow through reactor. The swelling ratio of the gel rods during each oscillation cycle is dependent on the rod diameter. Gel rods of smaller diameters exhibited larger swelling ratios. The linear swelling ratio of a 50 mum diameter rod is 80% and close to the equilibrium swelling ratio. Buckling is observed for gel rods with large swelling ratios. A chemomechanical walker is constructed by adding two capillary legs to a rod comprised of poly(NIPAAm-co-MAAc) gel. The walker moves in a forward-backward-forward pattern, with movement that is highly directional. The translational direction is independent of the surface upon which the walker moves.;Quorum sensing refers to density-dependent gene-transcription regulation phenomena that occurs in certain bacteria colonies. The gene transcription can be turned on at high cell densities and off at low cell densities. A similar transition is observed in locally and globally coupled chemical systems. In a locally coupled system, ferroin-loaded beads are positioned to form a quasicircular monolayer covered by catalyst-free BZ solution. The catalyst BZ solution is composed of 0.10 M NaBr, 0.20 M MA, 0.60 M H2SO4 and varied concentration of NaBrO3. For solutions with NaBrO3 concentrations between 0.24 M and 0.30 M, chemical waves are observed only in groups with a bead number larger than a critical value. A transition from steady state to oscillatory behavior occurs when the size of the group increases. This transition has the features of a dynamical quorum sensing transition. Numerical simulations indicate that the quorum sensing transition is associated with a decrease in the loss of activator to the solution. In a globally coupled system, large populations of ferroin-loaded beads are stirred in a batch reactor at different stirring rates. A transition from steady state to oscillatory behavior is observed when the number density of the beads is increased at high stirring rate. A Kuramoto synchronization transition, where oscillators gradually synchronize as the number density increases, is observed at low stirring rate. Numerical simulations were in accord with both transitions observed experimentally at the corresponding exchange rates.

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