Core-Shell Structured Magnetite-Poly(diphenylamine) Microspheres and Their Tunable Dual Response under Magnetic and Electric Fields

Core-shell type poly(diphenylamine)-coated magnetite (Fe₃O₄-PDPA) microspheres were designed and adopted as a novel actively tunable smart material which is responsive under both electric and magnetic fields. Their morphology, chemical structure, crystalline structure, and thermal properties were characterized using scanning electron microscopy, transmission electron microscope, Fourier transform-infrared spectroscopy, X-ray diffraction, and a thermal gravimetric analyzer. Their magnetic and dielectric properties were determined using vibrating-sample magnetometer and an LCR meter, respectively. They were dispersed in silicone oil and their electrorheological (ER) and magnetorheological (MR) responses under the electric and magnetic fields, respectively, were examined. The formation of chain structure of Fe₃O₄-PDPA based E/MR fluid under the application of electric field or magnetic field was observed by an optical microscopy and the sedimentation stability was observed by a Turbiscan optical analyzer system. It was observed that the yield stress, ER efficiency, and leakage current density increased with an increase in the particle concentration, while the slope of the electric field-dependent yield stress decreased. Several models such as the Bingham model, Herschel-Bulkley model, and Cho-Choi-Jhon equations were used to describe the shear stress curves of the ER fluid; the curves fitted well. For the dielectric properties, the two types of ER fluids tested displayed the same relaxation time and distribution; however, the one with the higher concentration had a higher dielectric constant and polarizability. The Fe₃O₄-PDPA based MR fluid (10 vol %) exhibited typical MR properties. In addition, the Herschel-Bulkley model matched well with the shear stress curves under a magnetic field.

Microporous poly(glycidyl methacrylate-co-ethylene glycol dimethyl acrylate) microspheres: synthesis, functionalization and applications

As a new kind of functional material, micron-sized porous polymer microspheres are a hot research topic in the field of polymer materials.

Nanoparticles Functionalized by Conducting Polymers and Their Electrorheological and Magnetorheological Applications

Conducting polymer-coated nanoparticles used in electrorheological (ER) and magnetorheological (MR) fluids are reviewed along with their fabrication methods, morphologies, thermal properties, sedimentation stabilities, dielectric properties, and ER and MR characteristics under applied electric or magnetic fields. After functionalization of the conducting polymers, the nanoparticles exhibited properties suitable for use as ER materials, and materials in which magnetic particles are used as a core could also be applied as MR materials. The conducting polymers covered in this study included polyaniline and its derivatives, poly(3,4-ethylenedioxythiophene), poly(3-octylthiophene), polypyrrole, and poly(diphenylamine). The modified nanoparticles included polystyrene, poly(methyl methacrylate), silica, titanium dioxide, maghemite, magnetite, and nanoclay. This article reviews many core-shell structured conducting polymer-coated nanoparticles used in ER and MR fluids and is expected to contribute to the understanding and development of ER and MR materials.

Polyaniline Coated Core-Shell Typed Stimuli-Responsive Microspheres and Their Electrorheology

Functional core-shell-structured particles have attracted considerable attention recently. This paper reviews the synthetic methods and morphologies of various electro-stimuli responsive polyaniline (PANI)-coated core-shell-type microspheres, including PANI-coated Fe₃O₄, SiO₂, Fe₂O₃, TiO₂, poly(methyl methacrylate), poly(glycidyl methacrylate), and polystyrene along with their electrorheological (ER) characteristics when prepared by dispersing these particles in an insulating medium. In addition to the various rheological characteristics and their analysis, such as shear stress and yield stress of their ER fluids, this paper summarizes some of the mechanisms proposed for ER fluids to further understand the responses of ER fluids to an externally applied electric field.

Stimuli-Responsive Polymer-Clay Nanocomposites under Electric Fields

This short Feature Article reviews electric stimuli-responsive polymer/clay nanocomposites with respect to their fabrication, physical characteristics and electrorheological (ER) behaviors under applied electric fields when dispersed in oil. Their structural characteristics, morphological features and thermal degradation behavior were examined by X-ray diffraction pattern, scanning electron microscopy and transmission electron microscopy, and thermogravimetric analysis, respectively. Particular focus is given to the electro-responsive ER characteristics of the polymer/clay nanocomposites in terms of the yield stress and viscoelastic properties along with their applications.

Synthesis and characterization of SiO2/polyaniline/Ag core–shell particles and studies of their electrical and hemolytic properties: multifunctional core–shell particles

Three layers of conducting core–shell nanocomposite particles composed of SiO₂/polyaniline (PAni)/Ag were prepared in the presence of silicon dioxide (SiO₂) in an aqueous solution containing sodium dodecyl benzenesulfonate (SDBS) as a surfactant.

Core-shell-structured monodisperse copolymer/silica particle suspension and its electrorheological response

Monodisperse core-shell-structured poly(styrene-co-butyl acrylate-co-[2-(methacryloxy)ethyl] trimethylammonium chloride)/silica (PSBM/SiO2) nanoparticles were applied as new electrorheological (ER) materials in which the particles were dispersed in an insulating oil. These nanoparticles were prepared by the consecutive precipitation of cetyltrimethylammonium bromide and negatively charged tetraethylorthosilicate onto the cationic surfaces of PSBM colloidal particles. The successful deposition of the shell phase of the particles and their morphology was examined by transmission and scanning electron microscopy. Their ER properties were studied with a rotational rheometer under different shear modes: controlled shear rate, steady shear under constant shear rate, and creep test. The silica shell allowed the PSBM/SiO2 particles to exhibit typical ER performance under an applied electric field. The dielectric spectra of the PSBM/SiO2-based ER fluid were also recorded using an LCR meter, which was correlated to the ER performance of the ER fluid.

Development and characterisation of switchable polyaniline-functionalised flow-through capillary monoliths

Polymer monoliths were prepared in capillary format (250 μm i.d.) and used as solid supports for the immobilisation of the conducting polymer polyaniline (PANI).

Self-assembly behavior of amphiphilic poly(amidoamine) dendrimers with a shell of aniline pentamer

A series of amphiphilic poly(amidoamine) dendrimers (PAMAM, G2-G5) composed of a hydrophilic core and a hydrophobic shell of aniline pentamer (AP) were synthesized and characterized. The modified dendrimers self-assembled to vesicular aggregates in water with the critical aggregation concentration (CAC) decreased in the order of G2 > G3 > G4 > G5. It was found that the modified dendrimers self-organized into spherical aggregates with a bilayer vesicular structures and that the dendrimers in higher generation have more order structure, which may be attributed to the crystallization induced by the compacted effect of AP segments. In addition, larger spherical vesicles were observed under acidic and alkaline conditions, as compared with sizes of aggregates in neutral medium. At low pH, the tertiary amine groups of PAMAM-AP were transformed to ammonium salts; the polarons were formed from AP units by doping with strong acids, thereby leading to the stability of vesicular aggregates being better than that in double distilled water. Nevertheless, in high pH environment, the deprotonation of PAMAM-AP caused the enhancement of π-π interactions, resulting in generation of twins or multilayered vesicles.

Conducting Material-incorporated Electrorheological Fluids: Core-shell Structured Spheres

Conducting material-based electro-responsive particles have become important as the smart soft matter in electrorheological (ER) fluids. These materials include conducting polymers, such as polyaniline, polypyrrole and poly(3,4-ethylenedioxythiophene), and carbon materials, such as carbon nanotubes and graphene oxide. Core-shell structured ER particles containing these materials as either core or shell species have attracted increasing interest owing to their outstanding advantages of an enhanced ER effect or diverse ER mechanism, lighter particulate density and lower cost. This paper summarizes the recent advances in synthesis methods as well as the critical characteristics of the core-shell structured particles, such as shear stress, yield stress and dielectric properties.