Electric field induced self-assembly of mesoscale structured materials and smart fluids

This dissertation aims to study the forces that drive self-assembly in binary mixtures of particles suspended in liquids and on fluid-liquid interfaces when they are subjected to a uniform electric or magnetic field. Three fluid-particle systems are investigated experimentally and theoretically : (i) Suspensions of dielectric particles in dielectric liquids; (ii) Suspensions of ferromagnetic and diamagnetic particles in ferrofluids; and (iii) Dielectric particles on dielectric fluid-liquid interfaces. The results of these studies are then used to estimate the parameter values needed to assemble materials with desired mesoscale microstructures. The first fluid-particle system studied is an electrorheological (ER) fluid formed using a mixture of positively and negatively polarizable particles. An important property of ER fluids is that their rheological properties can be modified on demand, within a few milliseconds, by applying an external electric field. Then, after the field is switched off, they go back to their original state. However, if only positively or negatively polarizable particles are used, the distribution of particles will fragment into chains and columns. Experimental results show that if a suitable mixture of positively and negatively polarized particles is used for making the ER fluid, the particle chains come closer, and the volume they occupy decreases. These results agree with the direct numerical simulations (DNS) based on the Maxwell Stress Tensor (MST) and point dipole methods. The application of the electric field results in the formation of a closely packed three-dimensionally connected structure. The influence of varying the electric field intensity, particle size, polarizabilities, and number ratio are characterized in terms of the extent of connected pattern formation which is obtained numerically and the experimentally measured yield stress. The yield stress for an ER fluid formed using a particle mixture is larger than that for an ER fluid containing only one type of particles and ...