Previous research has shown that polyhedral oligomeric silsesquioxane (POSS) particles in silicone oil show electrorheological (ER) activity. The effect of the number of same functional groups attached to POSS cage structures on the ER activity of these structures is discussed in this article. Two compounds of the octahedral geometry (T8) of cyanopropyl POSS (cPOSS) were used for this investigation. One of the compounds (monofunctionalized cPOSS) was commercially available, and the other (octafunctionalized cPOSS) was synthesized. The effects of the number of cyanopropyl functional groups attached to the inorganic silicon-oxygen core structure of the POSS compounds on the rheological properties are demonstrated through steady flow and oscillatory tests. Particular attention is paid to how the number of cyano functional groups affects the behavior of these suspensions of cPOSS compounds in silicone oil under increasing electric field strength. The research also contributed answers to the effects of changing the concentration of the cPOSS particles in the suspension. The flow curve was described by the Herschel-Bulkley model, and the yield stress values were ascertained from the model. The dielectric characterization was also done to support the ER response results, which showed that the octafunctionalized compound gave a better response. The differences in the ER properties of these compounds have also been discussed with the tests.
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