The comparison between carboxyl, amido and hydroxy group in influencing electrorheological performance

Three kinds of electrorheological (ER) materials with carboxyl, amido and hydroxyl group, respectively, were synthesized by a simple adsorption method. The powder of silicon dioxide as a substrate of the materials, as well as terephthalic acid [ p -C 6 H 4 (COOH) 2 , abbr.: phen-COOH], p -phenylenediamine [ p -C 6 H 4 (NH 2 ) 2 , abbr.: phen-NH 2 ] and hydroquinone [ p -C 6 H 4 (OH) 2 , abbr.: phen-OH] were chosen as starting materials. The ER properties of suspensions of the materials in silicon oil were studied. The suspension of the material adsorbing phen-COOH reveals the highest ER activity, the relative shear stress of the suspension (25 wt%), τ r (=τ E /τ 0 , τ E and τ 0 are the shear stresses at electric field strengths of E=4.2 and 0 kV/mm, respectively), reaches 220 under a DC electric field at a shear rate of 14.5 s −1 . The shear stress of the suspension of the material adsorbing phen-NH 2 is the largest at an high electric field strength. The ER activity of the material adsorbing phen-OH is the lowest among the three materials. The molecule structure is an importance factor in influencing ER performance of the materials for similar compounds with different polar function groups. The relationship between the ER activity and dielectric property of the materials was discussed.