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Title: Crystallisation and phase separation in colloidal systems
Author: Martelozzo, Virginie C.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2001
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We have studied the ageing of the crystal structure of model hard-sphere suspensions, using the light scattering equivalent of powder X-ra crystallography. By suspending the same colloidal particles in two different mixtures of solvents, we were able to tune the effect of gravity acting of the crystallites. The crystalline structure after nucleation and growth is found to be RHCP in all conditions. Over time a very slow rearrangement of the RHCP structure towards a more fcc-like ordering is observed in 'normal gravity', while in reduced gravity (increased buoyancy), the crystals retain their initial RHCP structure. A detailed study also shows that the crystal structure is affected by very small mechanical disturbances. We find that perturbations incurred during manual handling of the samples act as 'stimuli' to fcc nucleation. The phase behaviour of these hard sphere colloidal suspensions becomes even more intriguing on addition of non-adsorbing polymer. The effect of the polymer can be described by adding a polymer-induced attractive 'depletion' potential to the bare hard-sphere interaction. Above certain polymer to colloid size ratio, a critical point is found to emerge in the phase diagram. There is an unresolved discrepancy on the value of this crossover size ratio predicted by theory and observed experimentally. A detailed study of the phase separation kinetics by time-lapse video recording, using bright and dark field imaging, shows a complex behaviour, including the interplay of wall crystallisation with bulk equilibrium phase separation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available