Electrorheology of polyaniline-coated inorganic particles in silicone oil

Pickering Emulsion Polymerized Polyaniline/Zinc-ferrite Composite Particles and Their Dual Electrorheological and Magnetorheological Responses

A functional raspberry-like core-shell composite particle consisting of a conducting polyaniline (PANI) core and magnetic zinc ferrite shell is synthesized by Pickering emulsion polymerization. The morphology and chemical structure of the PANI/zinc-ferrite composite are evaluated by scanning electron microscopy, transmission electron microscopy, and Fourier-transform infrared spectroscopy. An electrorheological/magnetorheological fluid consisting of the PANI/zinc-ferrite composite dispersed in silicone oil with a particle concentration of 5 vol % is fabricated. Its rheological characteristics under external electric and magnetic fields are investigated by using a rotational rheometer. Under the electric or magnetic field, the PANI/zinc-ferrite particles form chain-like structures, demonstrating a solid-like state.

Guided self-assembly of nanostructured titanium oxide

A series of nanostructured titanium oxide particles were synthesized by a simple wet chemical method and characterized by means of small-angle x-ray scattering (SAXS)/wide-angle x-ray scattering (WAXS), atomic force microscope (AFM), scanning electron microscope (SEM), transmission electron microscope (TEM), thermal analysis, and rheometry. Tetrabutyl titanate (TBT) and ethylene glycol (EG) can be combined to form either TiO(x) nanowires or smooth nanorods, and the molar ratio of TBT:EG determines which of these is obtained. Therefore, TiO(x) nanorods with a highly rough surface can be obtained by hydrolysis of TBT with the addition of cetyl-trimethyl-ammonium bromide (CTAB) as surfactant in an EG solution. Furthermore, TiO(x) nanorods with two sharp ends can be obtained by hydrolysis of TBT with the addition of salt (LiCl) in an EG solution. The AFM results show that the TiO(x) nanorods with rough surfaces are formed by the self-assembly of TiO(x) nanospheres. The electrorheological (ER) effect was investigated using a suspension of titanium oxide nanowires or nanorods dispersed in silicone oil. Oil suspensions of titanium oxide nanowires or nanorods exhibit a dramatic reorganization when submitted to a strong DC electric field and the particles aggregate to form chain-like structures along the direction of applied electric field. Two-dimensional SAXS images from chains of anisotropically shaped particles exhibit a marked asymmetry in the SAXS patterns, reflecting the preferential self-assembly of the particles in the field. The suspension of rough TiO(x) nanorods shows stronger ER properties than that of the other nanostructured TiO(x) particles. We find that the particle surface roughness plays an important role in modification of the dielectric properties and in the enhancement of the ER effect.

Synthesis and electrorheological behavior of sterically stabilized polypyrrole–silica–methylcellulose nanocomposite suspension

Various polypyrrole (PPy)-silica-methylcellulose nanocomposite particles were synthesized by suspension polymerization in the presence of silica nanoparticles controlling the ratio of pyrrole, silica, and methylcellulose during the polymerization. The electrorheological (ER) and dielectric properties of the sterically stabilized PPy-silica-methylcellulose nanocomposite suspensions were investigated. The ER response increases with the increase in the silica/pyrrole ratio. The ER behavior also depends on the methylcellulose amount during the polymerization. The yield stress initially increases with the methylcellulose amount, passes through a maximum, and then decreases with the methylcellulose amount. The dielectric constants and dc conductivities of the PPy-silica-methylcellulose nanocomposite particles and the dielectric properties of their suspensions indicate that the increased ER response arises from the enhanced interfacial and particle polarization which depends on the silica/pyrrole ratio and the methylcellulose amount during the polymerization.