Date of Award

12-2009

Degree Name

Doctor of Philosophy

Department

Mechanical and Aeronautical Engineering

First Advisor

Dr. Muralidhar Ghantasala

Abstract

Stimuli-responsive gels are three-dimensional, cross-linked polymeric materials that undergo large physical change in response to the environmental stimuli, like temperature, pH, electrical potential, and irradiation. Ferrogels are colloidaldispersion of magnetic nanoparticles in the hydrogel network. The magnetic nanoparticles are attached to the polymeric network by different adhesive forces; as a result, it becomes sensitive to the applied magnetic field.

The main objective of this research is the simulation, synthesis, and characterization of the hydrogel and ferrogel. Simulation of the hydrogel response was performed for various environmental stimuli using a multiphysics finite element analysis software, COMSOL. The pH and electrical response of the hydrogel in steady state and transient conditions are investigated. These simulations also include the preliminary results of the ferrogel response in the magnetic field. Ferrogels were synthesized using magnetite (Fe304) and meghamite (Fe203) nanoparticles in the range 5 nm to 50 nm. These investigations included process optimization, characterization, and correlation of properties with process parameters. These samples are characterized by Ultra Small Angle X-ray Scattering, Transmission Electron Microscopy, Differential Scanning Calorimetry,DC Superconducting Quantum Interference Device magnetometer for the particle distribution, temperature phase transition, and magnetization.

Simulation of the hydrogel response to the external stimuli pH, and an electric field has successfully been demonstrated. The effect of buffer concentration and the fixed charge density on the swelling characteristics are studied in varying pH condition. In addition, the pH responsiveness is simulated for the chemical sensing reactive- hydrogels, like blood glucose level sensing. Gel synthesis used Design of Experiment methods to optimize the cross-linking (1-8%), and particle-loading parameters (1-14%) for N-Isopropylacrylamide based gels in the presence of magnetic fields. Lower particle size (>10nm) Fe3O4 surfactant layer coated particles provided single particle distributions without any unwanted agglomeration and aggregate distributions. Magnetic moments of the gels were found in the range 0.5 to 5 emu/gram depending on different synthesis parameters with relatively stable phasetransition temperature around 33°C. Overall, the dissertation has been successful in simulation of these stimuli-responsive gels and established new methodology of correlation using different characterization techniques.

Access Setting

Dissertation-Open Access

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