Hybrid polyaniline-coated sepiolite nanofibers for electrorheological fluid applications

Hybrid materials constituted by sepiolite covered with polyaniline (PAni) with different compositions have been prepared using two simple methods: bulk and slurry oxidative polymerization. The hybrid nanofibers were characterized by Fourier transform-infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), thermo-gravimetric analysis (TGA), electrical conductivity, dielectric spectroscopy analysis and electrorheological response. Fiber-based nanocomposites with PAni nanoparticles well adhered to the sepiolite surface were successfully prepared by slurry polymerization. The best recovering of the nanofibers was observed in nanocomposites containing 46 wt% of PAni, (SP 50:50s sample) as indicated by FTIR and TEM and quantified by TGA analysis. Also the best electrorheological response was obtained with the corresponding suspensions containing 10 wt% of the hybrid material suspended in castor oil. The values of the field induced shear modulus in the linear viscoelastic region: G′ = 536 kPa at E = 2 kV/mm is higher than those found for the suspensions of pure components, PAni or sepiolite, and one of the best values obtained with conventional ER fluids. A model to estimate the interaction between two nanofibers has been proposed considering the length and thickness of the nanofiber, calculated by TEM.