RUI: Field-Induced Phase Transitions in Monodisperse Ferrofluid Emulsions

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9321201 Liu The proposal is to explore experimentally the rich phase behavior exhibited in a confined colloidal suspension, a monodisperse ferrofluid (oil-in-water) emulsion. An externally applied magnetic field induces a large magnetic moment in each droplet, leading to a transition of the suspension from a fluid-like phase to a more ordered phase. The various phases can consist of separated chains, ordered columns, or a complex labyrinthine pattern. The evolution of the structure that forms, and its dependence on various key parameters will be investigated. These field induced structures dramatically modify the viscosity of the fluid, making this system an ideal model for a magnetorheological fluid. Thus the results are expected to lead to new insight into the fascinating phase behavior of these systems and provide guidelines for making technologically important materials with fundamentally new properties. %%% The proposal is to experimentally explore the phase behavior of a suspension of small droplets of oil immersed in water. Each oil droplet is uniform in size and contains thousands of tiny floating magnets. An externally applied magnetic field reorients the tiny magnets so that each droplet acts like a big magnet. This causes the droplets to line up into chains such that the suspension undergoes a phase transition. These field-induced new phases modify the viscosity of the fluid dramatically, turning the liquid into a solid which may lead to the development of actively controlled shock absorbers and clutches for cars or robotic joint controls. This research is to study the field-induced structural change of these systems and to provide guidelines for making technologically important materials with fundamentally new properties. ***