Abstract:

We will present experimental measurements of the effect of applied magnetic fields on the rheology of the polymer liquid crystal HPC/m-cresol. Parallel plate geometry and magnetic fields normal to flow deformation (vorticity) were used. Response of the polymer liquid crystal to applied magnetic fields was measured with a Superconducting Quantum Interference Device (SQUID). Magneto-rheometry measurements at shear rates of 0.1 to 10 1/s and magnetic fields of up to 0.7 T indicate an increase in viscosity upon application of the magnetic field, which is believed to be due to due to the aligning effect of the magnetic field on the HPC molecules. Shear thinning is observed for these liquid crystalline samples, even under applied magnetic fields. In addition, novel tumbling behaviors were observed with the external applied fields. Incorporation of magnetic nanoparticles (to obtain a ferronematic) resulted in a larger increase in viscosity upon application of external DC magnetic fields.  For these suspensions SQUID measurements showed a ferronematic that possessed magnetic hysteresis. To our knowledge a fluid with magnetic hysteresis has not been previously reported.

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