Anomalous and Instable Ultrasonic Evidence for a Structural Phase Transition at the Critical Value Vc in Electrorheological Suspensions

Abstract

Using the sample cell designed by ourselves and the electrorheological (ER) samples, one of them is imported from USA (sample 1), the other one is made from tsinghua university (sample2), we perform a series experiments with these two ER samples, and observe some curious phenomena; such as the ultrasonic study on the longitudinal sound velocity in electrorheological (ER) suspensions reveals the existence of a serious shear instability at the critical value of applied voltages, the evidence retains the time of about a few milliseconds; moreover, the experiments on ER samples demonstrate that there is a saturation value for the ultrasonic attenuation when the applied voltages arrive a critical value Vc, which resemble to the cases of a lot of superconductors at the critical value of temperature Tc; In the experiments on the I-V characteristic of the two ER samples, we observe that an abrupt change in the I-V characteristics occurs at the critical value Vc of the applied voltages, furthermore, the I-V characteristic of either of the two ER samples is linear after the applied voltages overpass the critical value Vc, just as same as the I-V characteristic of metal conductors. Therefore, it is reasonable to suggest that this anomalous ultrasonic evidence we observed in the experiments corresponds to a structural phase transition from liquidlike phase to metal-solidlike phase in the electrorheological suspensions.