Chemical and Biomolecular Engineering - Theses

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Author: Homer, Stephen Henry × Type: PhD thesis × Subject: rheology ×

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    Hierarchical structure function relationships in biopolymer systems
    Homer, Stephen Henry ( 2023-03)
    Biopolymer networks are assemblies of biopolymer chains that form into a coherent self-supporting structure and on the macro-scale appear as gels. These biopolymers often assemble in a very specific manner exhibiting various structures at different length scales. Thus, a structural hierarchy exists. This work investigates whey protein isolate as a model biopolymer system to establish the relationship between the 3D microstructure and the mechanics of the network. The molecular, aggregate, and micro through to macroscopic assemblies of these materials leads to their complex physical and rheological properties. The structure at multiple length scales has been examined using a range of techniques including but not limited to x-ray scattering, circular dichroism, and microscopy. The rheological properties of the gels and aggregate suspensions resulting from preparation methods incorporating heating, pH adjustment and shear is reported. Particular attention focuses on the application of shear forces during gelation and the effects on the microstructure, aggregation behaviour, particle sizes, and rheological properties of the resulting protein suspensions and gels produced during heating has been investigated. Models have been proposed to explain the results. A key finding from this work relates to the role of effective concentration, resulting from an interplay between nominal concentration and pH, in determining the outcome during biopolymer microparticulation. The use of small-scale perturbations to augment gel rheology was also examined with effects such as strain hardening being introduced into otherwise non-strain hardening gels. This research brings new insights to structural design principles and opens avenues to control the mechanics of gelled systems and the sizes of aggregates resulting from microparticulation.