Ying Dan Liu

Graphene oxide coated core–shell structured polystyrene microspheres and their electrorheological characteristics under applied electric field

Core–shell structured polystyrene (PS)–graphene oxide (GO) microspherical particles were synthesized by adsorbing the GO sheets on the PS surface through a strong π–π stacking interaction. As core materials, monodispersed PS microspheres were prepared using a dispersion polymerization, while the shell part of GO was synthesized by a modified Hummers method. Morphology of the composite particles was studied by both scanning electron microscopy and transmission electron microscopy, while their structure and chemical components were examined viaX-ray diffraction and Fourier-transform infrared spectroscopy, respectively. All the data confirmed the coexistence of PS and GO with the expected core–shell structure of the composite. In addition, for the study on the electroresponsive behavior, the composite was dispersed in silicone oil and its electrorheological (ER) characteristics were examined via both an optical microscope and a rotational rheometer which was equipped with a high voltage source. Without an electric field, it behaved like a fluid, however, when an external electric field is present, the particles became polarized and demonstrated typical chain-like ER structures.

Electrorheological fluids: smart soft matter and characteristics

An electrorheological fluid, a special type of suspension with controllable fluidity by an electric field, generally contains semiconducting or polarizable materials as electro-responsive parts. These materials align in the direction of the applied electric field to generate a solid-like phase in the suspension. These electro-responsive smart materials, including dielectric inorganics, semiconducting polymers and their hybrids, and polymer/inorganic composites, are reviewed in terms of their mechanism, rheological analysis and dielectric characteristics.

Core-shell structured semiconducting PMMA/polyaniline snowman-like anisotropic microparticles and their electrorheology.

Core-shell structured semiconducting snowman-like particles were synthesized, and their electrorheological (ER) characteristics under an applied electric field were examined. Monodispersed snowman-like poly(methyl methacrylate) (PMMA) particles were fabricated previously using a seed emulsion polymerization procedure. These anisotropic particle-based ER fluids, which were tested using a rotational rheometer, exhibited unusual ER properties in the flow curves at various electric field strengths when analyzed using the Cho-Choi-Jhon model. The dielectric spectra, as supporting data for the ER effect, were measured using a LCR meter. The relaxation time of the ER fluid was relatively shorter than typical ER fluids.

Core-shell structured carbonyl iron microspheres prepared via dual-step functionality coatings and their magnetorheological response.

The dispersion stability of soft magnetic carbonyl iron (CI)-based magnetorheological (MR) fluids was improved by applying a unique functional coating composed of a conducting polyaniline layer and a multiwalled carbon nanotube nest to the surfaces of the CI particles via conventional dispersion polymerization, followed by facile solvent casting. The coating morphology and thickness were analyzed by SEM and TEM imaging. Chemical composition of the polyaniline layer was detected by Raman spectroscope, which also confirmed the coating performance successfully. The influence of the functional coating on the magnetic properties was investigated by measuring the MR performance and sedimentation properties using a vibrating sample magnetometer, rotational rheometer, and Turbiscan apparatus. Improved dispersion characteristics of the MR fluid were observed.

Electrorheology of Graphene Oxide

Novel polarizable graphene oxide (GO) particles with oxidized groups on their edge and basal planes were prepared by a modified Hummers method, and their electro-responsive electrorheological (ER) characteristics when dispersed in silicone oil were examined with and without an electric field applied. The fibrillation phenomenon of this GO-based electro-responsive fluid was also observed via an optical microscope under an applied electric field. Both flow curves and dielectric spectra of the ER fluid were measured using a rotational rheometer and a LCR meter, respectively. Its viscoelastic properties of both storage and loss moduli were also examined using a vertical oscillation rheometer equipped with a high voltage generator, finding that the GO-based smart ER system behaves as a viscoelastic material under an applied electric field.

Silica nanoparticle decorated polyaniline nanofiber and its electrorheological response

We fabricated polyaniline nanofibers (PANIFs) with an average diameter of 350 nm through an interfacial polymerization by using dodecylbenzylsulfate acid as a dopant, and then examined their electrorheological (ER) characteristics. Silica modification was carried out in ethanol/water solution via a modified Stober method, and successful location of the silica nanoparticles on the surface of PANIF was confirmed by both scanning electron microscope (SEM) and transmission electron microscope (TEM) images. Thermogravimetric analysis (TGA) showed enhanced thermostability of the modified nanofibers. ER tests including flow curve and amplitude/frequency sweeps, which were performed by a rotational rheometer, demonstrated that the nanosilica modified PANIF exhibits higher ER effect than pure PANIF. In addition, the resultant flow curves are fitted well by Cho–Choi–Jhon model rather than Bingham model, while the yield stresses of both ER fluids versus electric field strengths are fitted well into a single line by the universal yield stress equation.

Smart monodisperse polystyrene/polyaniline core–shell structured hybrid microspheres fabricated by a controlled releasing technique and their electro-responsive characteristics

We synthesized core/shell structured monodisperse semi-conducting polystyrene/polyaniline (PS/PANI) composite microspheres, and studied their electro-responsive electrorheological (ER) performance under an applied electric field strength when dispersed in silicone oil. An over-layer of the conducting PANI is formed by a controlled releasing process of the aniline pre-adsorbed on the PS seed latex without any surface modification, in which the PS seed microspheres were readily prepared by a dispersion polymerization method. The PS microspheres are observed to be regularly encapsulated with PANI from the morphology test. The ER behaviors of the hybrid microspheres are characterized using a rotational rheometer equipped with a high voltage supplier. The yield stress and flow response as a function of shear rate under certain electric field strengths are investigated using the universal yield stress equation and the Cho–Choi–Jhon model of rheological equation of state, respectively. The relaxation time and achievable polarizability of the fluid from its dielectric analysis were also found to be well correlated with the ER performance of the ER fluid.

Pickering-Emulsion-Polymerized Polystyrene/Fe2O3 Composite Particles and Their Magnetoresponsive Characteristics

Core-shell-structured magnetic polystyrene (PS)/inorganic particles were fabricated by Pickering emulsion polymerization using nanosized Fe2O3 particles as a solid stabilizer. Scanning electron microscopy and transmission electron microscopy confirmed the synthesized PS/Fe2O3 particles to be comprised of a PS surface coated with Fe2O3 nanoparticles. The chemical structure of the composite nanospheres was characterized by Fourier transform infrared spectroscopy and X-ray diffraction. The thermal properties of composite nanospheres and corresponding pure polymer were examined by thermogravimetric analysis. The rheological properties of the core-shell-structured magnetic PS/inorganic particles dispersed in silicone oil were investigated under an external magnetic field strength using a rotational rheometer. The particles with extremely lower density than common magnetic particles exhibited solid-like magnetorheological phase characteristics, and the flow curves were fitted to the Cho-Choi-Jhon model of the rheological equation of state.

Magnetic field intensity effect on plane electric capacitor characteristics and viscoelasticity of magnetorheological elastomer

Magnetorheological (MR) elastomer was prepared using silicone rubber and soft magnetic carbonyl iron microspheres, and then examined as dielectric materials for manufacturing electric capacitors. As a specific element, capacity of the capacitors located in a magnetic field was found to be sensitive to both the MR suspension proportion to the silicone rubber and the intensity of the applied magnetic field. Viscoelastic characteristics of the MR elastomer, represented by storage modulus and creep behavior, were also studied.

Core-Shell Structured Monodisperse Poly(3,4-Ethylenedioxythiophene)/Poly(Styrenesulfonic Acid) Coated Polystyrene Microspheres and Their Electrorheological Response

We report the successful synthesis of transparent thin film of conducting poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS) coated monodisperse polystyrene (PS) microspheres via a simple physical adsorption route in an aqueous media and their electrorheological (ER) application under an applied electric field. Due to the insulating PS core, the PEDOT/PSS wrapped PS (PEDOT/PSS/PS) particles possess a low volume conductivity appropriately applied as ER active materials. Tested by a rotational rheometer under an applied electric field, the PEDOT/PSS/PS based ER fluid dispersed in a silicone oil shows a typical Bingham-fluid behavior with increased yield stresses according to the increase of electric field strength.