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Title: Phase separation and gelation in biopolymer mixtures
Author: Anderson, V. J.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2000
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This thesis examines a system consisting of two biopolymers, gelatine (a protein that forms a gel under certain conditions of temperature and concentration) and dextran (a non-gelling polysaccharide) in solution. At high temperatures the polymers are miscible but at low temperatures (less than ˜35°C) phase separation and gelation can occur. This thesis investigates this phenomenon using light scattering, microscopy and rheology. It is shown that very different structure are formed depending on the relative rates of phase separation and gelation. At high temperatures the gelation occurs slowly and confocal microscopy experiments have revealed that droplets of one phase in another result. At low temperatures the gelation occurs quickly and, for a sample in which the two polymers are present in similar quantities, an interconnected structure is produced. The evolution of these different structures is examined using several techniques, the main method being small angle light scattering, and analysed within the framework of several theories describing phase separation, the key one being the Cahn-Hilliard theory of spinodal decomposition. This theory was found to describe the early stages of phase separation well in spite of the effects of gelation, indicating the resilence of the underlying physical processes even in the presence of the molecular reorganisation that occurs in gelation. Effects of the gelation are seen at low temperatures (˜18°C), the principal effect it has is to alter the characteristic lengthscale produced in the sample - deeper quenches producing shorter lengthscales. In the later stages of phase separation the gelation has a more obvious effect, altering the mechanisms of the coarsening of the structure. In samples poor in gelatine coalescence of the droplets could occur, in others the gelation of the gelatine within the droplets prohibited coalescence over the period of observation. Rheology experiments also showed differences between samples quenched to different temperatures, the modulus of the sample depending to some extent on the concentration of gelatine in the continuous phase. The compositions of the phases produced were functions of temperature and the rates of phase separation and gelation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available