Temperature dependence of particle-particle interactions in electrorheological fluids

We report on the temperature dependence of particle-particle interactions i n electrorheological (ER) fluids for the temperature range 20-100 degrees C . The attraction force between polyamide spheres immersed in silicone oil i s measured as a function of temperature. The force-temperature characterist ic shows a broad maximum around 40 degrees C, corresponding to an increase of about 30% compared to the force measured at room temperature. In view of these results we proposed that the temperature dependence of the shear str ess in ER fluids is directly related to the variation of the local particle -particle attraction forces. Data are discussed in light of models which we re proposed in the literature to describe particle-particle interactions. A t high electric fields "conduction models" could explain the observed tempe rature dependence through the variations of the oil breakdown field with te mperature. However, limitations of such models are also clearly evidenced b y data obtained at low electric fields. (C) 2000 American Institute of Phys ics. [S0021-8979(00)00207-3].