ELECTRORHEOLOGY OF DISPERSIONS OF BaxSr(1-x) TiO3 IN SILICONE OIL UNDER AC OR DC ELECTRIC FIELD

Electrorheology (ER) of ferroelectric materials such as nanometric BaTiO3 is still not fully understood. In this paper, nanoparticles of BaxSr(1-x) TiO3 (where x = 0.8, 0.9 or 1.0) were synthesized using the method of Pechini, calcinated at 950 degrees C, and after, lixiviated under pH 1 or pH 5. A controlled stress rheometer (MCR-301) was used to make the ER characterization of dispersions made of BaxTi1-xO3 in silicone oil (30% w/w), where (a) shear stress as a function of DC electric field (under constant shear rate) or (b) shear stress as a function of shear rate (under constant AC or DC electric field) were measured. We observed that electrophoresis occurred under electric field DC, creating a concentration gradient which induced phase separation in ER fluid. On the other hand, under AC fields above 1 kV/mm, the ER effect is stronger than for DC field, and almost without electrophoresis. Furthermore, there is an AC frequency, dependent on the disperse phase, where the ER effect has a maximum.