Dielectric Polarization and Electrorheological Response of Poly(ethylaniline)-Coated Reduced Graphene Oxide Nanoflakes with Different Reduction Degrees

We prepared poly(ethylaniline)-coated graphene oxide nanoflakes and then treated them with different concentrations of hydrazine solution to form dielectric composite nanoflakes having different reduction degrees of reduced graphene oxide core and insulating polyethylaniline shell (PEANI/rGO). The morphology of PEANI/rGO was observed by scanning electron microscopy, while the chemical structure was confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectrometer. The influence of reduction degrees on the conductivity, dielectric polarization and electrorheological effect of PEANI/rGO in suspensions was investigated by dielectric spectroscopy and rheological test under electric fields. It shows that the PEANI/rGO has two interfacial polarization processes respectively due to rGO core and PEANI shell. As the number of hydrazine increases, the conductivity and polarization rate of rGO core increase. As a result, the difference between the polarization rate of rGO core and that of the PEANI shell gradually becomes large. This increased difference does not significantly decrease the yield stress but causes the flow instability of PEANI/GO suspensions under the simultaneous action of electric and shear fields.

The Effect of Dielectric Polarization Rate Difference of Filler and Matrix on the Electrorheological Responses of Poly(ionic liquid)/Polyaniline Composite Particles

By using different conductivity of polyaniline as filler, a kind of poly(ionic liquid)/polyaniline composite particles was synthesized to investigate the influence of dielectric polarization rate difference between filler and matrix on the electrorheological response and flow stability of composite-based electrorheological fluids under simultaneous effect of shear and electric fields. The composite particles were prepared by a post ion-exchange procedure and then treated by ammonia or hydrazine to obtain different conductivity of polyaniline. Their electrorheological response was measured by dispersing these composite particles in insulating carrier liquid under electric fields. It showed that the composite particles treated by ammonia had the strongest electrorheological response and most stable flow behavior in a broad shear rate region from 0.5 s−1 to 1000 s−1. By using dielectric spectroscopy, it found that the enhanced electrorheological response with stable flow depended on the matching degree of the dielectric polarization rates between poly(ionic liquid) matrix and polyaniline filler. The closer their polarization rates are, the more stable the flow curves are. These results are helpful to design optimal composite-based electrorheological materials with enhanced and stable ER performance.

Nonconservative Rayleigh scattering

Context. The continuous spectrum of stellar and planetary atmospheres can be linearly polarized by Rayleigh or Thomson scattering. The polarization rate depends on the ratio κc/(κc + σc), κc and σc being the absorption coefficients due to photo-ionizations and scattering processes, respectively. The scattering process is conservative if κc = 0, and in this case the center-to-limb variation of the polarization rate follows Chandrasekhar’s law. Deviations from this law appear if the scattering is nonconservative, that is, if photons have a probability ϵ = κc/(κc + σc) of being destroyed at each scattering. Aims. Nonconservative Rayleigh scattering is addressed here with a perturbation point of view, using ϵ, assumed to be a constant, as an expansion parameter. The goal is to obtain a perturbation expansion of the polarized radiation field that can be used to measure of the effects of a nonzero ϵ on the polarization rate of the emergent radiation and to check the accuracy of numerical codes. Methods. The expansion method is an application to Rayleigh scattering of a general perturbation approach developed for scalar monochromatic transport equations. The introduction of a space variable, rescaled by a factor √ϵ, transforms the radiative transfer equation into a new equation from which one can extract simpler equations to describe the field in the interior of the medium and in boundary layers. Results. The perturbation method is applied to a plane-parallel slab with no incident radiation and an unpolarized primary source of photons. The interior and boundary layer fields are expanded in powers of √ϵ. The expansion of the interior radiation field shows that it is unpolarized at leading order, with an intensity i0(τ̃) satisfying a diffusion equation, and that the polarization appears at order ϵ. The emergent radiation is calculated up to and including order ϵ. The leading term yields the polarization rate of the Chandrasekhar’s law. The following one, of order √ϵ, accurately predicts the decrease of the polarization rate for values of ϵ up to 10−3 and shows that it varies roughly as (1 − μ) for any unpolarized primary source. Methods for testing the accuracy of numerical schemes are proposed. The perturbation method is also applied to a slab with an incident radiation field and a polarized primary source of photons.

SELF-ASSEMBLY MORPHOLOGIES AND ELECTRORHEOLOGICAL PROPERTIES OF POLYANILINE-POLY(ETHYLENE GLYCOL)- POLYANILINE TRIBLOCK COPOLYMERS

The self-assembly properties and ER effects of the Polyaniline-Poly(ethylene glycol)-Polyaniline (PAn-PEG-PAn) triblock copolymers were studied in this paper. The results indicate that with the increase of solubility parameter of the solvent, PAn-PEG-PAn copolymers form into different morphologies of spheriods, vesicles and rods. PAn-PEG-PAn copolymers with vesicles morphology show the highest polarization strength, while those with rods have the most rapid polarization rate. Among the PAn-PEG-PAn copolymers of different morphologies, the PAn-PEG-PAn copolymer vesicles show the strongest ER effect.