Efficient and stable electrorheological fluids based on chestnut-like cobalt hydroxide coupled with surface-functionalized carbon dots

Intrinsically polarized electrorheological fluids (ERFs) have better thermal stability than ERFs with polar molecules, so they have a broader application prospect. However, the electrorheological efficiency of the common intrinsically polarized ERF is still lower than 1500, which is related to the poor wettability between polarized materials and the continuous phase. Carbon dots (CDs) exhibit good stability, semiconductor properties and low toxicity. We prepared biomimetic chestnut-like cobalt hydroxide coupled with surface-functionalized CD particles (Co(OH)₂@CDs) by a simple hydrothermal method. Then we prepared an ERF by mixing Co(OH)₂@CDs with silicone oil and studied the effect of CDs on its rheology and electrorheology properties. The synergistic effect of the lipophilic groups on the surface of CDs and the biomimetic chestnut-like structure makes Co(OH)₂@CDs exhibit good wettability with silicone oil, and the optimal zero-field viscosity of Co(OH)₂@CDs-ERF is only 0.46 Pa s (particle mass fraction of 40%). Exceptional electrorheological efficiency (about 10 000, shear rate 0.1 s^-1, 5 kV mm^-1) and dynamic shear stress stability of optimal Co(OH)₂@CDs-ERF can be attributed to the dielectric enhancement of the biomimetic chestnut-like structure coupled with the semiconductor properties of CDs. In addition, Co(OH)₂@CDs-ERF has excellent anti-settling performance, outstanding thermal stability and low current density.

1D and 2D hybrid polymers based on zinc phenylphosphates: synthesis, characterization and applications in electroactive materials

The synthesis, structure and properties of three hybrid polymers based on zinc arylphosphates are described in this study. Zinc bis(diphenylphosphate) (ZnDPhP) was obtained as needle-like crystals containing hexagonally packed, homochiral 1 ∞[Zn(DPhP)2/2] helical chains. The XRD and DSC studies revealed that upon heating, ZnDPhP undergoes a reversible thermal transition at ca. 160 °C with expansion mainly perpendicular to its c-axis. Zinc phenylphosphate hydrate (ZnMPhP-H) formed plate-like particles with an average thickness of less than 1 μm and much thinner nanolayers with a basal spacing of 15.5 Å. ZnMPhP-H was easily and reversibly dehydrated to its anhydrous form, ZnMPhP-A, which exhibited a somewhat larger basal spacing of 16.5 Å and the capacity for amine intercalation. The thermal decomposition of ZnDPhP or ZnMPhP-A began around 250 °C, resulting in the formation of solid mixtures of zinc phosphates and electron-conducting carbonaceous phases. The bulk electrical conductivities of the poly(vinylidene fluoride)-based composites containing the ZnDPhP pyrolyzates reached 0.1-0.2 S cm-1. Upon mixing with silicone oil, all the synthesized hybrid polymers formed fluids that exhibit significant negative electrorheological effects and have potential for application in electroresponsive smart materials. The application of an electric field during the crosslinking of such systems affected the viscoelastic properties of the resultant solid composites, while the cured systems showed rather small electrorheological effects.

Recent development of electro-responsive smart electrorheological fluids

The characteristics of an electrorheological (ER) fluid, as a class of smart soft matter, can be actively and accurately tuned between a liquid- and a solid-like phase by the application of an electric field. ER materials used in ER fluids are electrically polarizable particles, which are attracting considerable attention in addition to further research. This perspective reports the latest ER materials along with their rheological understanding and provides a forward-looking summary of the potential future applications of ER technology.

Electrorheology of SI-ATRP-modified graphene oxide particles with poly(butyl methacrylate): effect of reduction and compatibility with silicone oil

Surface-initiated atom transfer radical polymerization (SI-ATRP) was used to modify graphene oxide (GO) particles with poly(butyl methacrylate) (PBMA) chains. This procedure facilitated the single-step fabrication of a hybrid material with tailored conductivity for the preparation of a suspension in silicone oil with enhanced sedimentation stability and improved electrorheological (ER) activity. PBMA was characterized using various techniques, such as gel permeation chromatography (GPC) and ¹H NMR spectroscopy. Thermogravimetric analysis through on-line investigation of the Fourier transform infrared spectra, together with transmission electron microscopy, X-ray photoelectron microscopy, and atomic force microscopy, were successfully used to confirm GO surface modification. The ER performance was investigated using optical microscopy images and steady shear rheometry, and the mechanism of the internal chain-like structure formation was elucidated. The dielectric properties confirmed enhanced ER performance owing to an increase in relaxation strength to 1.36 and decrease in relaxation time to 5 × 10⁻³ s. The compatibility between GO and silicone oil was significantly influenced by covalently bonded PBMA polymer brushes on the GO surface, showing enhanced compatibility with silicone oil, which resulted in the considerably improved sedimentation stability. Furthermore, a controlled degree of reduction of the GO surface ensured that the suspension had improved ER properties.

Surface-initiated atom transfer radical polymerization (SI-ATRP) was used to modify graphene oxide (GO) particles with poly(butyl methacrylate) (PBMA) chains.

High-Performance Magnetorheological Suspensions of Pickering-Emulsion-Polymerized Polystyrene/Fe3O4 Particles with Enhanced Stability

The magnetorheological (MR) performance of suspensions based on core-shell-structured foamed polystyrene (PSF)/Fe₃O₄ particles was investigated by using a vibrating sample magnetometer and a rotational rheometer. Core-shell-structured polystyrene (PS)/Fe₃O₄ was synthesized by using the Pickering-emulsion polymerization method in which Fe₃O₄ nanoparticles were added as a solid surfactant. Foaming the PS core in PS/Fe₃O₄ particles was carried out by using a supercritical carbon dioxide (scCO₂) fluid. The density was measured by a pycnometer. The densities of PS/Fe₃O₄ and PSF/Fe₃O₄ particles were significantly lowered from that of the pure Fe₃O₄ particle after Pickering-emulsion polymerization and foaming treatment. All tested suspensions displayed similar MR behaviors but different yield strengths. The important parameter that determined the MR performance was not the particle density but rather the surface density of Fe₃O₄ on the PS core surface. The morphology was observed by scanning electron microscopy and transmission electron microscopy. Most Fe₃O₄ particles stayed on the surface of PS/Fe₃O₄ particles, making the surface topology bumpy and rough, which decreased the particle sedimentation velocity. Finally, Turbiscan apparatus was used to examine the sedimentation properties of different particle suspensions. The suspensions of PS/Fe₃O₄ and PSF/Fe₃O₄ showed remarkably improved stability against sedimentation, much better than the bare Fe₃O₄ particle suspension because of the reduced density mismatch between the nanoparticles and the carrier medium as well as the surface topology change.

The normal stress of an electrorheological fluid in compression mode

This work studied the normal stress of an ER fluid in compression mode through both experiment and simulation.

Tunable electrorheological characteristics and mechanism of a series of graphene-like molybdenum disulfide coated core–shell structured polystyrene microspheres

Core–shell structured molybdenum disulfide (MoS₂) coated polystyrene (PS) microspheres are synthesized with the help of hexadecyl trimethyl ammonium bromide (CTAB) through negative–positive electrostatic attraction.

Graphene oxide modified by betaine moieties for improvement of electrorheological performance

Novel graphene oxide bearing betaine moieties as sulfobetaine (GO-SB), carboxybetaine (GO-CB) and carboxybetaine ester (GO-CBE) moieties were prepared in two simple fabrication processes based on silanization and a thiol–ene click-reaction.

Latex routes to graphene-based nanocomposites

This review article describes recent advances in the elaboration of graphene-based colloidal nanocomposites by the use of graphene or graphene oxide in heterophase polymerization systems.

Facile synthesis of polyaniline nanotubes and their enhanced stimuli-response under electric fields

Polyaniline (PANI) nanotubes were fabricated successfully using a micelle soft-template method in the presence of oxalic acid as a dopant and applied as the dispersed phase of an electrorheological (ER) fluid.