Poly(diphenylamine)/polyaniline core/shell composite nanospheres synthesized using a reactive surfactant and their electrorheology

Relatively monodispersed poly(diphenylamine)/polyaniline (PDPA/PANI) core/shell composite nanospheres were fabricated by an oxidative polymerization, both in the dispersed phase of diphenylamine and at the interface between the suspended and continuous phases. A reactive surfactant synthesized with aniline and sodium dodecyl sulfate was adopted. The fine core/shell structure formation via pi-pi stacking between the aromatic rings of PDPA and PANI was confirmed by analyzing the chemical composition, morphology, and crystallinity of the particle components. An electrorheological (ER) fluid was fabricated by suspending the PDPA/PANI nanoparticles in silicone oil, and its ER behaviors were characterized by the controlled shear stress and rate, dynamic oscillation, and on-off electrical field tests. The ER fluid under an electric field exhibited an immediate phase transition, viscoelasticity, and three measurement-dependent yield stresses. In addition, its stable shear stresses over a wide range of shear rates were fitted smoothly by the CCJ model and were shown to increase with increasing EF strength. Moreover, the dielectric characteristics and Cole-Cole analysis of the ER fluid confirmed the effective ER property. The PDPA/PANI-based ER fluid possessing an instantaneous and controllable electro-response is believed to be a promising system for intelligent control applications.