| The first part of this thesis reports advances in the preparation and handling of colloidal suspensions of Tobacco Mosaic Virus and observations of their properties in the nematic and colloidal crystalline phases. We observe that a spatially periodic distortion occurs as the initial response of a liquid crystal to a large reorienting field. Measurements of the wavelength of the distortion as a function of magnetic field strength and direction are presented. A linear analysis of the equations of motion of the nematic yields the growth rate of the distortion. We guess that the observed periodicity is the wavelength that grows the fastest initially and that at later times non-linear effects, not included in our theory, act to suppress all other wavelengths. The exact form of the distortion is shown to be a function of the geometry of the sample, the boundary conditions, the visco-elastic constants and the strength of the magnetic field. These transient responses will occur in all nematics under quite easily obtainable conditions.;At high fields, association of the spheres is irreversible as long as the field is on. When the field is turned off the particles diffuse apart. The chains are flexible, and within one chain, field dependent fluctuations in the sphere-sphere separation are observed. At low fields the association of particles is reversible.;Using digital microscopy, we measured the equilibrium and non-equilibrium distribution of chain lengths of polystyrene spheres and also measured the dynamics of a pair of associating particles. We calculated the equilibrium distribution and the average separation between particles within one chain. The dynamics of association is described using the Smoluchowski equation. During intermediate stages of irreversible aggregation, the chain length distribution assumes a scaling form typical of diffusion limited aggregation.;The second part of the thesis presents experimental studies of micron diameter polystyrene spheres suspended in an aqueous medium and confined to a thin layer to which a high frequency uniform electric field in the plane of the sample is applied. A suspension of spheres in an electric field undergoes linear aggregation, forming clusters of spheres resembling pearl chains. |
