The electrorheological effect of polyaniline nanofiber, nanoparticle and microparticle suspensions

Polyaniline (PANI) is an important electrorheological (ER) material. In this paper, PANI with different morphologies, including nanofiber, nanoparticle and microparticle, are prepared on a large scale by a simple and modified oxidative polymerization method in a low-cost citric acid aqueous solution. The effect of particle morphology on the electric, ER, sedimentation, and temperature properties of PANI suspensions is investigated systematically. The results show that the suspensions containing PANI nanofibers and nanoparticles possess significantly improved suspended stability compared to the suspension containing PANI microparticles. Under electric fields, however, the PANI nanofiber suspension exhibits the strongest ER effect. Its yield stress is about 2.5-3.0 times as high as that of the PANI nanoparticle suspension and 1.3-1.5 times as high as that of the PANI microparticle suspension. The shear stress of the PANI nanofiber suspension maintains this more stable level in the wide shear rate region of 0.1-1000s^-1 as compared to that of the PANI nanoparticle and microparticle suspensions. Furthermore, the temperature test shows that the PANI nanofiber suspension can maintain a good ER effect in a wide temperature range like the PANI microparticle suspension, while the temperature stability of the PANI nanoparticle suspension is reduced, possibly due to smaller particle size.