ELECTRORHEOLOGICAL PROPERTIES OF BATIO3 SUSPENSIONS

Electrorheological (ER) fluids based on a silicone oil matrix with a h igh dielectric constant particulate component, BaTiO3, were evaluated. Particle size effects were examined with a commercial BaTiO3 (0.35mum in size) and a hydrothermally prepared BaTiO3 powder with an average particle size of 0.07mum. The commercial powder exhibited an ER respon se to DC fields, but above a critical field strength rheological prope rties dropped off drastically. The relative magnitude of yield stresse s, at field levels below the critical field strength, are comparable w ith current literature values. Hydrothermally prepared BaTiO3 powder e xhibited minimal ER response to applied DC fields. Optical microscope studies of dilute suspensions (approximately 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 f ibril formation with a maximum level occurring around 60Hz. In respons e to AC fields, both types of BaTiO3 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 formati on with increased AC field strength (60Hz). Turbulent flow did not app ear with increased AC field (60Hz) at all field strengths evaluated (l ess-than-or-equal-to 20kV/cm). All suspensions exhibited a linear rela tionship between yield stress and the square of applied electric field , which is characteristic of dipole-dipole interactions.