Experimental studies and computational simulations of the anisotropy of the magnetoviscous effect in ferrofluids

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The research project aims to investigate the anisotropy of the magnetoviscous effect in ferrofluids by experimental studies using a slit die viscometer. In the previous part of the project, suitable ferrofluids were selected and characterized and a slit die viscometer was built that allows measurements of all three viscosity coefficients, meaning for a magnetic field oriented in the direction of the flow or the shear gradient or in the neutral direction, without Rosensweig instabilities interfering. A special magnetic coil system provides a notably strong and homogeneous magnetic field so that both ferrofluids with strong interparticle interactions and ferrofluids with weak interparticle interactions could be studied. In the experiments undertaken in the previous phase it could be shown, that significant differences between weakly and strong interacting fluids concerning the magnetoviscous effect and its anisotropy exist. Change in the viscosity coefficients and their relations depending on field strength and mechanical load applied could be explained on the basis of structure formation of the magnetic particles. Moreover a test-rig for the synthesis of particles for new taylor-made mono- and bidisperse ferrofluids using an ultrasonic aerosol pyrolysis process has been build up and tested. Respective fluids are planned to be used in the last project phase. For the final project phase dedicated experiments are planned to prove the microscopic hypotheses for the observed magnetoviscous effects and to relate them to the microstructure of the fluids. Therefore ferrofluids containing differently sized particles - having thus different interparticle interaction -, bidisperse particle mixtures or rod like model particles will be employed.