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Title: Microstructural studies of clay dispersions and gels
Author: Houghton, H. A.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2007
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Clay-water mixtures are interesting materials with a large number of commercial applications. Many clays form gels at very low volume fractions (<1%) and the structure of these gels is still under discussion. This work explores the gelation and resulting microstructures with a novel combination of environmental scanning electron microscopy (ESEM), particle tracking techniques and microrheology. Using ESEM a range of clay suspensions and gels were studied. Due to attenuation of the electron beam by surface water, it was not possible to image the microstructures of clays in solution. Attempts were made to quantify the depth of water through which imaging is possible. The microstructures of Attapulgite, Bentonite, Hectorite and Kaolin, both dry and after suspension in water (followed by the necessary evaporation of water), are qualitatively compared. In the case of rigid, non-swelling clays the microstructure revealed by in-situ evaporation of water retains some structural information.  Using a suspension of Gibbsite a protocol is developed allowing a quantitative study of microstructural changes induced on changing the pH and ionic strength of the suspension. The observed changes are in accordance with the clay literature. Application of the protocol to Kaolin revealed qualitative microstructural changes. Particle tracking techniques and microrheology were used to study the gelation of Hectorite. These methods rely on the analysis of the Brownian motion of tracer particles (added to the Hectorite). Sample heterogeneity, gel times and viscoelastic moduli were studied, with minimal sample perturbation. Different regimes of concentration, pH and ionic strength were studied and results were consistent with standard models of clay gelation found in the literature.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available