Natalia V. Blinova

Effect of hydrophilicity of polyaniline particles on their electrorheology: steady flow and dynamic behaviour.

Electrorheological properties of suspensions are considerably affected by hydrophilicity of suspension particles. As a model material, polyaniline base powder protonated with sulfamic, tartaric, or perfluorooctanesulfonic acids provided particles of various hydrophilicity. The experiments revealed that, in the absence of electric field, due to a good compatibility of hydrophobic polyaniline particles with silicone-oil medium, their interactions were limited and the viscosity of suspension was low. When the electric field was applied, the rigidity of the polarized chain structure of the particles increased and, consequently, viscosity increased as well. In the contrast, the field-off suspension viscosity of highly interacting hydrophilic particles, which are incompatible with the oil, and where particle aggregation may set in, was high especially at low shear rates, and the material had a pseudoplastic character. Then, a relative increase in viscosity due to the polarization of the particles or their clusters in the electric field was much lower than in the former case. Due to a different primary structure of suspension, depending on the particle compatibility with the oil the field-off storage modulus of suspensions of hydrophobic particles was lower than the loss modulus, while in suspensions of hydrophilic particles the former modulus dominated. In both cases, an increase in elasticity with increasing electric field strength was higher than that in viscosity.

The Effect of Compatibility of Suspension Particles With the Oil Medium on Electrorheological Efficiency

The compatibility of solid phase–liquid medium appears to be an important factor for controlling the electrorheological (ER) efficiency of ER fluids. Controlled protonation of polyaniline particles with perfluorooctanesulfonic, tartaric, or sulphamic acid provides particles in a broad range of hydrophobicity as a suitable model to study this phenomenon. The relation between organization of such particles in silicone oil suspensions in on/off electric field at rest and during flow at various volume concentrations was demonstrated.

The role of particle conductivity in electrorheology of suspensions of variously protonated polyaniline

Electrorheological behaviour of silicone oil suspensions of particles of polyaniline protonated to various doping level with orthophosphoric 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 unlike particle permittivity especially at higher protonation degree is dominant in polarization process. 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.