The electrorheological efficiency of polyaniline particles with various conductivities suspended in silicone oil

Electrorheological (ER) behavior of silicone oil suspensions of particles of polyaniline protonated to various doping levels with ortho-phosphoric and tetrafluoroboric acids has been studied. The dynamic yield stress obtained by extrapolation of shear stress to zero shear rate using Herschel–Bulkley equation was used as a criterion of the ER efficiency. At a same molar concentration of doping acids, various protonation effects appeared and the dependences of the yield stress on the acid concentration differed. The comparison of the yield stresses with dielectric characteristics calculated from the Havriliak–Negami equation revealed that the particle conductivity, in contrast to particle permittivity, dominates the polarization process especially at higher protonation degrees. Consequently, particle conductivity or dielectric relaxation time proved to be the parameters providing the common dependences of the yield stress regardless of the way of polarization.