Preparation and electrorheological properties of polyquin(2,3-b)acridine-12,14(5,7)dione-based suspensions

Novel polymeric electrorheological (ER) fluids were achieved by dispersing polyquin(2,3-b)acridine-12,14(5,7)dione (polyquinacridinedione, PQA) in bromodiphenylmethane (BDPM) and silicon oil, respectively; the conjugated polymer, PQA was synthesized via sequentially condensation, cyclization and oxidation from m-phenylenediamine and dimethyl 2,5-dioxocyclohexane-1,4-dicarboxylate. The structure characteristics of the PQA molecule and ER activity of the PQA-based suspensions were investigated. The results indicate that the PQA suspensions exhibited excellent ER activity both in BDPM and in silicon oil; the yield stress of the 30 wt.% PQA suspension in BDPM reaches up to 4 kPa under 3 kV/mm. The yield stress of the suspensions increases with the dielectric constant of the liquid media. The excellent ER activity of the suspensions is attributed to the unique molecular structure of PQA: the non-localized π bond and polarizable groups within PQA molecule, as well as the plane ladder-like structure of PQA molecule, leading to high polarization of the particles of PQA, and forming strong fibrillated chain- or even net-like assembly under electric field, which leads to remarkable yield stress. The results also show that, for the PQA suspension in DBPM, the yield stress is proportion to the squared electric field and weight percent of particles, the apparent viscosity linearly increases with the squared electric field.