Chemical and Biomolecular Engineering - Theses

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Start date: 2000 × End date: 2019 × Subject: rheology × Type: PhD thesis × Author: Rodd, Andrew B. ×

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    Characterisation of xanthan based, polymer solutions, physical gels and permanent networks
    Rodd, Andrew B. ( 2001)
    Gels and the gel transition are topics that have been the subject of extensive and widespread academic and industrial interest. Polymer gels and particularly those involving biopolymers are extensively applied in the food, pharmaceutical, agricultural, photographic, oil recovery and paper industries. Such widespread commercial application is responsible for the academic and industrial interest in gaining a greater understanding of the intrinsic physics governing the behaviour of these systems. Rheological analysis of biopolymer based gelling systems is an invaluable tool for investigating fundamental properties as well as replicating processing and application conditions. Through combination of careful rheological analysis with techniques capable of probing molecular structure and dynamics, such as static and dynamic light scattering (LS), it is possible to develop structure-function relations that are considered critical in understanding and controlling gels and gelation of biopolymer systems. This thesis utilises the biopolymer xanthan gum, to investigate both rheologically and optically, polymer solutions, physical gels and permanent networks. A physical gel is one in which the interactions between molecules, responsible for the gel like properties, are not permanent, that is they have a finite timescale. Subsequently, on long enough time scales, a physical gel will flow. Alternatively, a permanent network, as the name suggests, is one in which the interactions (or crosslinks) are thermodynamically stable, and the system will therefore never flow. Aqueous xanthan solutions in the presence of mono or divalent cations will produce a solution with 'weak-gel' physical properties. A 'weak-gel' is a term commonly applied to structured fluids that on short time-scales possess properties allowing them to appear more 'gel like', however on longer timescales, they will flow. Conversely, on the addition of trivalent metal ions (and for the purposes of this work, aluminum ions Al(III)) , xanthan will form a strong thermally stable permanent network. Using rheological and light scattering (LS) techniques, this thesis, will consider the similarities and differences of xanthan based physical gels and permanent networks. (From Abstract)