Study of dynamics and structure of anisotropic colloidal suspensions using confocal laser scanning microscopy

Although understanding of the phase behavior, assembly and dynamics of spherical colloids interacting through isotropic potentials is advanced, comparatively little is known about such properties of anisotropic suspensions. In this dissertation, we experimentally investigate the role of one kind of anisotropy, shape anisometry, on the assembly and dynamics of colloids. By application of the direct visualization methodology of confocal laser scanning microscopy, we discover new features of the behavior of colloidal rods with regards to their dynamics in dilute solution and their assembly under applied fields. These results are applicable to the application of anisometric particles in materials with orientational order, such as colloidal liquid crystals.We developed a direct visualization method to characterize rotational and translational movement of colloidal rods in three dimensions. The method was applied to study the rotational and translational dynamics of dilute rod suspensions. The Brownian motion of rods in the solution was characterized by measuring the probability distributions of displacements for translation and rotation in addition to mean diffusivities. Experimental values were found to be in good agreement with theoretical predictions and errors in the method were fully characterized.The assembly of colloidal rods was achieved by application of an applied gravitational field of variable strength in a refractive index matched solvent. The quality of the orientational ordering was quantified by direct measurement of the order parameter. Although very different effects of the applied field strength were found for rods of high and low aspect ratio, all the measurements were found to be consistent with a primary mechanism for orientational ordering based on the local volume fraction of the sediment relative to the equilibrium isotropic to nematic transition. A role of the rod glass transition in the effect of the applied field on the sediment volume fraction was also inferred from the measurements. The effect of attractive pair potential interactions due to depletion forces on the assembly of rods during sedimentation (under gravitational field) was investigated. We found that depletion interactions combined with gravitation enhanced the orientational ordering of the sediments at particular, optimum concentrations of non-adsorbing polymer.