Evidence of nematic phases in electrorheological fluid by acoustic impedance measurement

Phase transitions of an electrorheological (ER) fluid were studied by measuring its shear specific acoustic impedance with increasing electric field. Two nematic phases were found for the first time in experiment and they confirmed the theoretical prediction. It is proved that measuring acoustic impedance is a unique way to study the structure formation in non-transparent ER fluids where the optical techniques are not available. The measuring results also demonstrate that ER fluids have potential of being active impedance matching devices.