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Title: Structure formation in colloidal rod suspensions : experiments and computer simulations
Author: Cordova, Claudia Elena Ferreiro
ISNI:       0000 0004 6057 8445
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2016
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Clay mineral particles have been widely used to prepare colloidal suspensions, certain clay mineral have a rod-like shape. Colloidal suspensions of thin rods are known to show nematic phases, provided that particles are well stabilised against attractive interactions. At low concentrations such suspensions are in the isotropic phase; the nematic phase can be found upon increase of concentration. In addition, isotropic configurations at volume concentrations similar to the ones in the nematic phase can be generated for thin rods. In these systems the particles are trapped in a disordered configuration called random packing. The present thesis studies the preparation of colloidal suspensions of rod-like particles as well as the bulk properties of systems composed of rod-like particles. Rod-like particle suspensions were prepared using sepiolite clay. The stabilisation of sepiolite particles in a non-polar solvent using a combination of surfactant and polymer treatment is reported. Here the effect of polar molecules, including water, on the surface of the treated clay particles is discussed. It is found that the effect of polar molecules on the bulk properties of the final suspensions is not negligible. The isotropic-nematic phase transition mechanism for polydisperse thin rods is also studied in this work using confocal microscopy. The samples studied have a large gap in concentration between the coexisting isotropic and nematic phases, that results from polydispersity. The time evolution of the phase separating samples was recorded using confocal images. Such images were binarized to identify isotropic and nematic regions in each image. Information on the structure was obtained from the binarized images. The phase separating samples did not show nucleation and growth, even at low concentrations. Instead, they phase separated via a percolating network formed by a transient "non-sticky gel". The behaviour observed in this work is most likely related to the high polydispersity of the particles used. Random packings of rod-like particles were generated using computer simulations of hard spherocylinders. An existing algorithm was modified and the new version produced reliable results with fewer adjustable parameters. The random packing configurations obtained were somewhat more dense than those reported previously. The same algorithm was applied to mixtures of hard spherocylinders and hard spheres. However, in this case the configurations obtained showed signs of order.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available