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Title: Colloidal gels under oscillatory shear
Author: Smith, Paul Andrew
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2004
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We have studied the quiescent structure of dense colloidal gels with varying strength of attraction with confocal microscopy. We have obtained high quality 3-D images that allow quantitative comparison of the different gels by the extraction of the 3-D particle coordinates and subsequent of quantitative measures of the local particle structure. We have observed that the gels have a liquid-like, although frozen in-homogeneous structure. We have found an increase in the average number of bonds per particle for decreasing attraction strength, accompanied by changes in the particle-free void regions. We developed and tested a precision linear parallel-plate oscillatory shear cell designed for light scattering-echo and microscopy experiments. This allows us to study in detail the response of gels with varying strength to low strain oscillatory shear at various frequencies will optical and confocal microscopy and light scattering-echo. We have found that the gels responds elastically to strains below a critical frequency and attraction potential dependent value. Above this critical strain the particles that make up the gel are formed to rearrange, for the strongest gels, small regions of crystal-like order can be induced by the shear and then frozen in place once the shear stops. For gels with lower potentials no ordered regions are observed in the timescale studied, however rearrangements of the voids were observed at lower strains for lower potentials. The apparent ordering is predominantly in 2-D planes and limited to small domains separated by defects or disordered particles. The amount of ordering is found to depend on strain and frequency. These results are interpreted by a simple model based on the timescale for a particle to escape from the potential well.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available