RHEODIELECTRIC SPECTROSCOPY ON HETEROGENEOUS POLYMER SYSTEMS - ELECTRORHEOLOGICAL FLUIDS

The technique of rheodielectric spectroscopy is used to investigate th e dielectric behaviour of electrorheological fluids (ERF) as a functio n of external electrical DC-field and/or shear rate. Commercial ERF's consisting of mesoscopic polyurethane particles in a silicone oil matr ix were studied. The particles contain a salt which leads to strong di pole moments via the Maxwell-Wagner-Polarization (MWP) if subjected to an external electrical held. In an electrical held the dipoles and, c oncomittantly, the particles motion become correlated leading to the f ormation of solid-like structures and significant changes in the visco sity. We demonstrate that dielectric spectroscopy is capable of monito ring the held and shear rate effects in terms of relaxation strength a nd relaxation time of the MWP. In electrical or shear fields dipole-di pole correlations increase the MWP's relaxation strength, so that we a re able to observe structure formation with dielectric spectroscopy, e specially the time resolved response of the ERF to changes in the elec trical held or the shear rate.