Electrorheological properties of BaTiO3 suspensions

Electrorheological (ER) fluids based on a silicone oil matrix with a high dielectric constant particulate component, BaTiO 3 , were evaluated. Particle size effects were examined with a commercial BaTiO 3 (0.35μm in size) and a hydrothermally prepared BaTiO 3 powder with an average particle size of 0.07μm. The commercial powder exhibited an ER response to DC fields, but above a critical field strength rheological properties dropped off drastically. The relative magnitude of yield stresses, at field levels below the critical field strength, are comparable with current literature values. Hydrothermally prepared BaTiO 3 powder exhibited minimal ER response to applied DC fields. Optical microscope studies of dilute suspensions (∼1-2 volume percent) were used to correlate fibril formation with ER measurements. Under applied DC fields, turbulent flow dominated above 6.25kV/cm and ER properties diminished. Increased frequency led to an increase in the degree of fibril formation with a maximum level occurring around 6OHz. In response to AC fields, both types of BaTiO 3 powders showed a strong frequency dependence. Maximum shear stress for a given field strength resulted at about 60Hz. Optical microscopy showed an increase in fibril formation with increased AC field strength (60Hz). Turbulent flow did not appear with increased AC field (60Hz) at all field strengths evaluated (≤20kV/cm). All suspensions exhibited a linear relationship between yield stress and the square of applied electric field, which is characteristic of dipole-dipole interactions.