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Title: Equilibrium and swelling properties of ion-sensitive holograms
Author: James, A. P.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2004
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Polymer gels could be used as chemical and biological sensors should the technology to measure their volume change in response to analytes be fully developed. Optical approaches based on thin films, synthetic opals, inverse opals and holographic sensors offer the opportunity to allow colorimetric analysis of polymer gel swelling. The diffraction from a holographic sensor with primary amine functionalities was found to be narrow band in wavelength, 15 nm, and angle, 0.7°, and the presence of side-lobes on the spectra were explained in terms of coupled wave theory. During pH-jump induced volume change the diffraction spectra from the holographic sensor developed crenulations which were dependent on hologram thickness and observation angle but largely independent of buffer strength. Through analysis of the kinetics and spectra an integrated model based on Crick’s solution for diffusion into a thin film could explain both the sigmoidal kinetics observed, and the spectral crenulations. The model described the initial rapid progress of an ionisation front moving through the gel, followed by the slow diffusion of analyte in a longer second phase. A panel of polymers containing primary amines and the carbonate ionophore trifluoroacetylbenzoate (TFAB) in poly(2-hydroxyethyl methacrylate). (pHEMA) and polyacrylamide (pAAm) copolymers was produced. Their response in relation to temperature, ionic strength, sulfate and aqueous carbon dioxide was examined. It was found that temperature responsive was a good indication of response to analytes. Which may, in-part, be due to the dominance of polymer-solvent mixing terms in determining response at high ionic strength. pHEMA holograms were insensitive to the identity and valency of the ions and pAAm was responsive to these conditions as determined by the relative “salting-out” potential of the ions. However, almost in contradiction to this trend, the influence of ionic strength was ten times lower on pAAm relative to pHEMA. The sensitivity to specific ions and the relative insensitivity of pAAm holograms suggest that pHEMA may have more potential as a basis for holographic sensors.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available