Synthesis and Characterization of Functional Mesostructures Using Colloidal Crystal Templating
Lee, Yun-Ju
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https://hdl.handle.net/2142/82763
Description
Title
Synthesis and Characterization of Functional Mesostructures Using Colloidal Crystal Templating
Author(s)
Lee, Yun-Ju
Issue Date
2005
Doctoral Committee Chair(s)
Braun, Paul V.
Department of Study
Materials Science and Engineering
Discipline
Materials Science and Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Optics
Language
eng
Abstract
Functional 3-D periodic mesostructures were synthesized via colloidal crystal templating, and their chemical, physical, and optical properties were characterized. By forming colloidal crystals through self-organization, infiltrating the interstitial space with functional materials, and removing the templates by chemical etching, inverse opal mesostructures with characteristic distances on the order of optical wavelengths were generated from conducting polymers, hydrogels, and metals. These active mesostructures allow tuning of properties such as Bragg diffraction, potentially enabling applications as electrochemical elements, sensors, flow control devices, and novel photonic band gap materials. Inverse opal conducting polymer films were fabricated by electropolymerization. The templated films exhibited a compact morphology and larger electrochemical response from cyclic voltammetry. They also displayed shifts in Bragg diffraction, possibly due to changes in interchain spacing and refractive index during redox cycling. Inverse opal hydrogels were templated using free radical photopolymerization. By copolymerizing appropriate functional groups, mechanically robust thin films were synthesized that exhibit reversible shifts in Bragg diffraction based on changes in solvent, pH, ionic strength, crosslink density, and glucose concentration, caused by the expansion and contraction of the hydrogel film due to changes in the local chemical potential. The kinetics of the diffraction response was found to be diffusion limited. The diffraction response of the inverse opal hydrogels was correlated to the deformations of their mesostructure directly observed using multiphoton fluorescence microscopy. Reconstruction of the pore mesostructure revealed that the hydrogel swelled primarily in the sample normal direction, with a significant shrinkage and deformation of the face centered cubic pores, consistent with predictions from scalar wave approximation. The results compared well with finite element modeling and indicated a change in crystallographic symmetry during hydrogel swelling. Inverse opal metallic films were fabricated via electrodeposition. Chemical etching of the metallic mesh were found to affect their optical properties, possibly enabling novel mesostructures that exhibit selective absorption and emission. By using colloidal crystal templating, tunable photonic mesostructures were synthesized and characterized. With direct observation of the mesostructure evolution through fluorescence microscopy and computational modeling of the physical and optical response, the relationship between the structure and properties of these photonic mesostructures was elucidated.
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