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Title: Jamming and the rheology of hard core colloids
Author: Farr, R. S.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1998
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This thesis is concerned with the behaviour under flow of concentrated spherical colloids with a central hard core. Chapters two to four deal with hard spheres in a Newtonian fluid, without conservative forces (such as buoyancy effects or polymer coats) or Brownian forces. The central observation from previous computer simulations is that when a simple shear startup flow is imposed on such a system at sufficiently high concentration, a steady state is not achieved: the dispersion locks up after a finite amount of strain, at which point the shear stress is divergent. These chapters develop and analyse a theoretical model for this 'jamming' behaviour, in terms of the percolation of clusters of particles forming near the compression direction of the simple shear flow. The previously observed sensitivity of rheology to short range particle interactions is discussed in the context of this clustering theory at the close of chapter four. As a concrete example, chapter five contains a related theory of clustering in weakly aggregating colloids, which leads to power law shear thinning, and which is compared to both computer simulations and experimental results from the literature. To illustrate the calculation of particle interactions, chapter six contains an analysis of the lubrication modes of a pair of sponge coated colloidal particles. Chapter seven considers the problem of the behaviour of disordered regions in a shearing crystal of colloidal particles, which is loosely related to the idea of clustering earlier in the thesis. In the last two chapters, we return to the behaviour of the final jammed states of the colloid, considered at the start of the thesis, when the system becomes a type of granular material. A review of some recent ideas in the field of stress propagation in static granular matter is presented in chapter eight, together with a discussion of a model material introduced here to illustrate some of the points at issue. Chapter nine then discusses a more sophisticated model of stress fluctuations in granular matter due to R.C. Ball, and the behaviour of the model under coarse graining is analysed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available