The article presents the results of in situ microscopic observations of quasihomogenic mixtures of hydrocarbon oils containing ionic liquids. Observations were made using NIKON ECLIPSE LV 100 D optical microscope. The mechanism of generating the ER effect in two mixtures was observed, i.e., in silicone damping liquid GP-1, which is polimethylsiloksane mixture containing 2% (v/v) of ionic liquid CJ 001, i.e., tetrafluoroboran 1-methyl-3-octyloxymethylimidazolium and base polialfaolefine oil PAO-6 which containing 2% (v/v) of ionic liquid CJ 008, i.e., trihexyltertradecylfosfonium bis(trifluoromethylsulfonyl) imide as well as in the two-component standard liquid LID3354s. The ob-servations carried out showed that the prepared mixtures had generated the ER effect. At the threshold value E = 0.3 kV·mm–1, the ER effect disappeared. Photographs, presented in the paper, show changes in the structure of mixtures containing ionic liquids that occur under the influence of an external elec-tric field, consisting in the formation of „fibril chains and/or fibril streams” and then, their destruction and accumulation of ionic liquid particles at the electrodes. Keywords: electrorheological effect (ER), lubricating oils, ionic liquids, microscopy.
