Electrorheological effect in suspensions of polyaniline

The electrorheological (ER) effect relies on the increase of viscosity of a fluid under electric field. The studied ER fluids (ERFs) were prepared out of silicone oil and polyaniline lightly protonated with four different acids of pKa values from −8 to +1.8. Rheological properties of the ERFs were measured under electric field up to 2.3 kV/mm. The influence of the protonation level of polyaniline and the acid used on the magnitude of the ER effect was studied. We propose an explanation of the observed relations based on measurements of dielectric properties of the polymers. The strongest ER effect was observed for polyaniline samples whose relaxation frequency was about 8 kHz, supporting the idea that the relatively slow polarisation processes were responsible for the ER effect. In addition, it was demonstrated that conductivity and dielectric constant of the polymers depended on the strength of the acids applied.