THE MEASUREMENT OF ULTRASONIC SHEAR-WAVE PROPERTIES IN ELECTRORHEOLOGICAL FLUIDS

Electrorheological (ER) fluid systems acquire reversible solid-like material properties upon the influence of a strong electric field. Prior efforts to study ER system properties acoustically have employed compressional waves. In this work, three ER systems have been studied by means of an ultrasonic shear wave reflectometry technique. In each case, a moderate to substantial increase in the shear wave velocity, storage modulus, and loss modulus was observed at the ER transition at 3 MHz. These results are interpreted in light of limited dynamic shear data at lower frequencies found in the literature, recent theoretical calculations, and direct observations using optical microscopy.