Shang Hao Piao

Facile and fast synthesis of polyaniline-coated poly(glycidyl methacrylate) core-shell microspheres and their electro-responsive characteristics.

Electro-responsive core-shell structured particles were fabricated in two steps. In the first step, a spherical and monodisperse poly(glycidyl methacrylate) (PGMA) core was prepared by dispersion polymerization with an epoxy group, which was then functionalized with an amine functional group (ami-PGMA) via an epoxide-amine reaction with ethylenediamine. In the second step, a conducting polyaniline (PANI) shell was grafted onto the ami-PGMA surface via the in situ polymerization of an aniline monomer with a uniform thickness. The epoxy group on the PGMA microspheres provided a simple and fast way to react with amine functional groups without the need for a further swelling or grafting process. The morphology of the core-shell structure was confirmed by scanning election microscopy and transmission electron microscopy. The electrorheological properties of the PGMA/PANI particles-based suspension were examined using a Couette-type rotational rheometer under an applied electric field. The shear stress curves were fitted to the Cho-Choi-Jhon (CCJ) model of the rheological equation of state.

Polyaniline/Fe composite nanofiber added softmagnetic carbonyl iron microsphere suspension and its magnetorheology

Fe0 nanoparticle-supported polyaniline (PANI) composite nanofibers were prepared as an additive for carbonyl iron (CI)-based magnetorheological (MR) fluids to improve the MR properties and dispersion stability. A simple chemical strategy was adopted to synthesize the PANI/Fe0 composite nanofibers. The synthesis method was based on the initial fabrication of interconnected PANI nanofibers by a rapidly mixed polymerization process using ferric chloride (FeCl3) as the oxidant and the subsequent reductive support of Fe0 nanoparticles onto the PANI nanofiber matrix using the polymerization by-products as a metal precursor. X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy showed that the fabricated nanofibers were composed of PANI and Fe0. Scanning and transmission electron microscopy imaging confirmed that the PANI/Fe0 composite nanofibers were 80–150 nm in diameter with an interconnected matrix. The MR fluid with the PANI/Fe0 composite nanofibers dispersed in mineral oil under an external magnetic field showed enhanced MR properties compared to that without an additive. Turbiscan data also confirmed the improved sedimentation properties of the MR fluid with an additive.

Electric Field-Responsive Mesoporous Suspensions: A Review

This paper briefly reviews the fabrication and electrorheological (ER) characteristics of mesoporous materials and their nanocomposites with conducting polymers under an applied electric field when dispersed in an insulating liquid. Smart fluids of electrically-polarizable particles exhibit a reversible and tunable phase transition from a liquid-like to solid-like state in response to an external electric field of various strengths, and have potential applications in a variety of active control systems. The ER properties of these mesoporous suspensions are explained further according to their dielectric spectra in terms of the flow curve, dynamic moduli, and yield stress.

Core-shell structured Fe3O4@SiO2 nanoparticles fabricated by sol–gel method and their magnetorheology

Using a sol–gel method, silica-coated magnetite (Fe3O4@SiO2) core-shell nanoparticles were fabricated following a two-step process. In the first step, the Fe3O4 nanoparticles were prepared via a solvothermal method. In the second step, the Fe3O4 nanoparticles were coated with SiO2 formed through the hydrolyzation of tetraethyl orthosilicate. The structure and properties of the core-shell Fe3O4@SiO2 nanoparticles were characterized and the results showed that Fe3O4@SiO2 nanoparticles are a soft magnetic material. A magnetorheological (MR) suspension was prepared based on the synthesized Fe3O4@SiO2 nanoparticles dispersed in silicone oil and measured using a rotational rheometer at various magnetic field strengths. Using a rotational rheometer, the MR properties of the Fe3O4@SiO2 in silicone oil, including shear stress, shear viscosity, and yield stress were examined under an applied magnetic field.

Magnetic Carbonyl Iron Suspension with Sepiolite Additive and Its Magnetorheological Property

Sepiolite, a fibrous clay mineral, was introduced to a soft magnetic carbonyl iron (CI) particle based magnetorheological (MR) fluid to improve its sedimentation problem, in which the MR fluid is a colloidal suspension of magnetizable particles dispersed in a nonmagnetic carrier. The MR characteristics of two MR fluid systems with and without a sepiolite additive were evaluated and compared under different magnetic field strengths using a rotational rheometer, exhibiting typical MR behaviors. Scanning electron microscopy images indicate that the sepiolite filled the interspaces among CI particles, therefore preventing a severe sedimentation problem and improving dispersion stability of the MR fluid. Sedimentation of the MR fluid was also characterized by an optical analyzer system of Turbiscan.

Additive role of attapulgite nanoclay on carbonyl iron-based magnetorheological suspension

Attapulgite (ATP), a fibrous nanoclay mineral, was adopted as an additive in this study to improve the sedimentation problem of soft magnetic carbonyl iron (CI)-based magnetorheological (MR) fluids caused by the density mismatch between the CI particles and medium oil. The MR characteristics of the two MR fluid systems with and without ATP were measured and compared using a rotational rheometer under different magnetic field strengths. Scanning electron microscopy indicated that ATP filled the interspaces among the CI particles, explaining the improved dispersion stability of the MR fluid based on the Turbiscan sedimentation measurements. Despite the slight decrease in MR characteristics, the MR fluid with the additive exhibited the typical MR performance of an increase in shear stress in an applied magnetic field.

Synthesis of kenaf cellulose carbamate and its smart electric stimuli-response

Cellulose carbamate (CC) was produced from kenaf core pulp (KCP) via a microwave reactor-assisted method. The formation of CC was confirmed by Fourier transform infrared spectroscopy and nitrogen content analysis. The degree of substitution, zeta potential and size distribution of CC were also determined. The CC was characterized with scanning electron microscopy, X-ray diffraction and thermogravimetry analysis. The CC particles were then dispersed in silicone oil to prepare CC-based anhydrous electric stimuli-responsive electrorheological (ER) fluids. Rhelogical measurement was carried out using rotational rheometer with a high voltage generator in both steady and oscillatory shear modes to examine the effect of electric field strength on the ER characteristics. The results showed that the increase in electric field strength has enhanced the ER properties of CC-based ER fluid due to the chain formation induced by electric polarization among the particles.

Stability Study of Flexible 6,13-Bis(triisopropylsilylethynyl)pentacene Thin-Film Transistors with a Cross-Linked Poly(4-vinylphenol)/Yttrium Oxide Nanocomposite Gate Insulator

We investigated the electrical and mechanical stability of flexible 6,13-bis(triisopropylsilylehtynyl)pentacene (TIPS-pentacene) thin-film transistors (TFTs) that were fabricated on polyimide (PI) substrates using cross-linked poly(4-vinylphenol) (c-PVP) and c-PVP/yttrium oxide (Y2O3) nanocomposite films as gate insulators. Compared with the electrical characteristics of TIPS-pentacene TFTs with c-PVP insulators, the TFTs with c-PVP/Y2O3 nanocomposite insulators exhibited enhancements in the drain current and the threshold voltage due to an increase in the dielectric capacitance. In electrical stability experiments, a gradual decrease in the drain current and a negative shift in the threshold voltage occurred during prolonged bias stress tests, but these characteristic variations were comparable for both types of TFT. On the other hand, the results of mechanical bending tests showed that the characteristic degradation of the TIPS-pentacene TFTs with c-PVP/Y2O3 nanocomposite insulators was more critical than that of the TFTs with c-PVP insulators. In this study, the detrimental effect of the nanocomposite insulator on the mechanical stability of flexible TIPS-pentacene TFTs was found to be caused by physical adhesion of TIPS-pentacene molecules onto the rough surfaces of the c-PVP/Y2O3 nanocomposite insulator. These results indicate that the dielectric and morphological properties of polymeric nanocomposite insulators are significant when considering practical applications of flexible electronics operated at low voltages.

Pickering emulsion polymerized magnetite-poly(methyl methacrylate) composite particles and their magnetorheology

Magnetic poly(methyl methacrylate) (PMMA)/Fe3O4 composite nanoparticles were fabricated by Pickering emulsion polymerization using nano-sized iron oxide (Fe3O4) particles as a solid stabilizer that had been synthesized initially from a hydrothermal process. High-resolution scanning electron microscopy was applied to characterize the morphology of the materials. Fourier transformation infrared spectroscopy confirmed the chemical structure of both pure Fe3O4 and PMMA/Fe3O4 composites. The magnetic properties and atomic and molecular structure of a crystal of the materials were examined by vibration sample magnetometry and X-ray diffraction, respectively. The magnetorheological (MR) features of both pure Fe3O4 and PMMA/Fe3O4 nanoparticles dispersed in mineral oil under a magnetic field were characterized by a rotational rheometer. The dynamic yield stress was higher than the elastic stress under external magnetic field. The PMMA/Fe3O4 composite-based MR fluid showed good dispersion stability, while exhibiting typical MR characteristics for the applied magnetic field dependent yield stress with a slope of 1.5.

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.