Santiago-Quiñones, Darlene I.

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    Magnetorheological characterization of magneto-responsive fluids
    (2012) Santiago-Quiñones, Darlene I.; Rinaldi, Carlos; College of Engineering; Acevedo, Aldo; Briano, Julio; Martinez-Iñesta, María; Department of Chemical Engineering; Collins, Danna
    The work presented in this dissertation focuses primarily on the rheological characterization of magneto-responsive fluids, consisting of suspensions of magnetic nanoparticles in non-magnetic liquid media. The rheology of these fluids has shown to be promising due to their enhanced viscous behavior when acted upon by external magnetic fields. This enhancement occurs due to a chaining of the nanoparticles, resulting in enhanced resistance to the applied shear. The rheology of magneto-responsive fluids with applied magnetic fields presented here, also known as magnetorheology, was studied for magnetoresponsive fluids such as ferrofluids, and for others were the suspending medium is a nonNewtonian fluid. For the case of ferrofluids, we have clarified the role of the particle’s magnetic relaxation mechanism and the magnetic aggregation effect on their magnetorheoloical behavior. The first study focused on two cases, a (i) rotating (Neél relaxation) and (ii) fixed (Brownian relaxation) magnetic moments and their effect on the balance between magnetic and hydrodynamic torques. The second study focused on the effect of magnetic field dependent aggregation behavior of the nanoparticles on the magnetrheology of these fluids. Magnetorheological studies of magneto-responsive non-Newtonian fluids where performed using polymer liquid crystals (ferronematics) and surfactants (magnetic surfactant solutions) as suspending media, reporting new types of magnetic soft materials. All these measurements were performed using a rheometer capable of applying magnetic fields and measuring rheological properties simultaneously such as viscosity flow curves, yield stresses, and storage and loss modulus (moduli), all magnetic field dependent.