Silicone Oil Suspensions Research Articles

Temperature-dependent electrorheological effect and its description with respect to dielectric spectra

Electrorheological fluids consisting of large number and type of electrically polarizable particles have been presented in the literature. Nevertheless, there is a lack of temperature-dependent electrorheological effect analysis, which is their major feature from the application point of view. In this work, aniline oligomers were synthesized and carbonized in order to obtain suitable materials to be used in electrorheological fluids. The silicone oil suspensions were prepared and their temperature-dependent electrorheological performance was investigated in the temperature range between 25°C and 65°C. The electrorheological fluid based on particles with larger size exhibits higher sensitivity to the increase in temperature than the electrorheological fluid based on smaller particles. As an evaluative tool, dielectric spectra of the prepared electrorheological fluids were investigated. It has been shown that the activation energy of the relaxation process is higher for the electrorheological fluid based on larger size particles. The enhanced electrorheological effect at high temperature was ascribed to the shift of dielectric relaxation of the electrorheological fluids to higher frequencies.

Graphene oxide reduction during surface-initiated atom transfer radical polymerization of glycidyl methacrylate: Controlling electro-responsive properties

Unique grafting of the poly(glycidyl methacrylate) from the surface of graphene oxide (GO) with the controllable reduction of GO particles was performed in a single-step reaction using atom transfer radical polymerization technique. The control of the GO surface reduction and modification can be achieved by appropriate selection of the ratio between tertiary amine and GO particle contents. Finely tuned electrical conductivity of the GO-PGMA particles enables simple tailoring of electro-responsive properties of their silicone oil suspensions.

The effect of sphere roughness on the rheology of concentrated suspensions

We present the results of measuring the viscometric flow of concentrated rigid-sphere suspensions with constant-viscosity matrices, both Newtonian (silicone oil) and non-Newtonian (Boger fluid: corn syrup (79.4%)–glycerin (19.8%)–4%PAA water (0.78%)). Various problems with the measurements are discussed, including settling due to density differences. The effect of sphere roughness on shear rheology is a main concern of the work. The viscosities of silicone oil and Boger fluid suspensions were increased by increasing sphere roughness, and the normal stress difference N1−N2 in the Boger fluid suspension also increased with roughness.

Magnetorheology of core-shell carbonyl iron/ZnO rod-like particle silicone oil suspensions under oscillatory shear

The aim of this study is a preparation and application of inorganic coating on the surface of carbonyl iron particles. The two step solvothermal synthesis provides core-shell CI/ZnO rod-like morphology. Compact coating of particles has a slightly negative impact on their magnetic properties (measured for magnetic field strength in the range from 0 to 213 mT); however, there is a suitable magnetorheological performance investigated under oscillatory shear, suitable to be applied in real applications.

Electrorheological performances of poly(o-toluidine) and p-toluenesulfonic acid doped poly(o-toluidine) suspensions

Poly(o-toluidine) (POT) and p-toluenesulfonic acid doped poly(o-toluidine) (TSA-POT) were synthesized via chemical oxidation and emulsion polymerization, respectively. The rheological measurements of the dedoped POT and TSA-POT silicone oil suspensions showed that both of the suspensions exhibited electrorheological (ER) effect under electric field. The analyses of the rheological curves of suspension indicated that POT and TSA-POT suspensions presented different flow behaviors. POT suspensions presented fast polarization under external electric field with the existence of critical shear rates (γcrit), and POT suspensions behaved well with Bingham model above γcrit TSA-POT suspension behaved very well with Cho–Choi–Jhon model in all shear rate regions. Both of static and dynamic yield stresses for POT and TSA-POT suspensions in electric field were proportional to the square of electric field strength. The different ER performances between POT and TSA-POT suspensions were explained based on the conductivity and dielectric constant of the particles. The modification of conductivity and dielectric constant by doping POT with TSA improved the ER performance of TSA-POT suspension.

Electrorheological characterization of dispersions in silicone oil of encapsulated liquid crystal 4-n-penthyl-4′-cyanobiphenyl in polyvinyl alcohol and in silica

The electrorheological (ER) effect is known as the change in the apparent viscosity upon the application of an external electric field perpendicular to the flow direction. In this work we present the electrorheological behaviour of suspensions in silicone oil of two different dispersed phases: foams of liquid crystal 4-n-penthyl-4′-cyanobiphenyl (5CB) encapsulated in polyvinyl alcohol (PVA) and nano/microspheres of 5CB encapsulated in silica. We will present the viscosity curves under the application of an electric field ranging between 0 and 3 kV mm−1. The ER effect was observed for the suspensions of 5CB/PVA but not in the case of 5CB/silica. For the case of the suspensions of 5CB/PVA, the effect of the viscosity of the continuum phase and the concentration of the dispersed phase was analysed, showing that the enhancement of the viscosity of the suspension increases with the concentration, as expected, however the continuum phase viscosity has no significant effect, at least in the investigated viscosity range.

The observation of a conductivity threshold on the electrorheological effect of p-phenylenediamine oxidized with p-benzoquinone

Preparation of 2,5-(di-p-PDA)-1,4-benzoquinone and the ER effect threshold of the silicone-oil suspensions.

Silica prepared in the presence of alkylphosphonium-based ionic liquids and its performance in electrorheological fluids

This work highlights the effect of silica particles prepared by a sol–gel process in the presence of different phosphonium-based ionic liquids on the electrorheological behavior of the corresponding suspension in silicone oil. The silica particles were prepared by hydrolysis/condensation of tetraetoxy silane (TEOS) in basic medium and in the presence of three different commercial ionic liquids: tri-isobutyl(methyl)phosphoniumtosylate (IL106), tri(n-butyl)(tetradecyl)phosphonium-dodecylbenzene-sulfonate (IL201) and trihexyl-(tetradecyl)-phosphonium-bis-2,4,4-(trimethylpentyl)-phosphinate (IL104). The resulting material was characterized by Fourier-transform infrared spectroscopy (FT-IR), thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM) and dielectric properties. The confinement of the ionic liquids inside the silica particles was suggested by thermogravimetric analysis. The presence of ILs also exerts a strong influence on the morphology and imparts good polarization ability to the silica. The electro-rheological response of the corresponding ionogel suspensions in silicone oil was investigated. A significant ER effect was observed for the fluid containing silica prepared in the presence of IL106. In fact, a very good response under the action of an electrical field corresponding to 3 kV mm−1 was achieved, with a shear stress value as high as 1215 Pa. This behavior may be attributed to the presence of the IL confined in the silica particles and also to the peculiar morphology which favors the formation of a columnar structure to a high extent.

Carbonization of aniline oligomers to electrically polarizable particles and their use in electrorheology

Abstract Aniline oligomers prepared via the oxidation of aniline under alkaline conditions at various concentrations of ammonia were carbonized at 650 °C in inert atmosphere. Subsequently, the prepared particles were mixed with silicone oil and the suspensions were used as electrorheological fluids. After the carbonization, when the higher amount of ammonia was present during the synthesis, the transition of morphology of the particles from microspheres to two-dimensional plates was observed. This transition led to a significant increase of viscosity of silicone-oil suspensions in the presence of external electric field, while their field-off viscosity remained nearly unchanged. Thus, the carbonization had the desired effect on the treated particles leading to extremely high electrorheological efficiency of the suspensions based on such particles. The highest electrorheological efficiency was achieved for the suspension based on carbonized particles prepared in 0.2 M ammonia. The dielectric spectroscopy was used as an evaluative tool of electrorheological performance of suspensions, and data correspond well with the obtained results from electrorheological experiments.

Rheological behaviors of fumed silica/low molecular weight hydroxyl silicone oil

ABSRACTThe structure and viscoelastic properties of fumed silica gels in low molecular weight hydroxyl silicone oil were investigated by means of steady and dynamic rheology. It is found that the fumed silica/hydroxyl silicone oil suspension exhibits shear‐thickening under steady shear and “strain‐thickening” under oscillatory shear condition. Effects of hydroxy groups on the rheological behavior of silicone oil suspension with highly dispersed hydrophilic amorphous silica were investigated by infrared, 1H‐NMR, and rheological test. The results show that the hydroxy groups on this system play an important role on the formation of shear thickening behavior of the suspension solution. At the same particle diameter and mass fraction, the amount of hydroxy groups on this system has a strong effect on increasing the viscosity of the suspension, which is likely due to multiassociation hydrogen bonding between liquid molecules and silanol groups on fumed silica surfaces (SiOH). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40722.

Effects of heating and shearing on the rheological properties of poly(tetra fluoro-ethylene) suspensions in silicone oil

The effects of heating and shearing on the rheological properties of poly(tetra fluoro-ethylene) (PTFE, 0.2μm particles) suspensions in silicone oil 1000cSt were investigated. The suspensions were heated at 140°C for 1 day and then sheared at a rate of 1000s−1 for 30min. Four suspensions were prepared: the unheated and unsheared suspension, the heated and unsheared suspension, the unheated and sheared suspension, and the heated and sheared suspension. Hysteresis loops, stress–strain (S–S) sweep curves, oscillatory dynamic moduli, and steady state shear flow curves of the suspensions were measured at 25°C. No hysteresis was observed in the hysteresis loops for any of the suspensions. Two yield stresses were observed in the S–S sweep curves of the unsheared suspensions. Shearing caused the lower yield stress to fade but retained the higher yield stress. The S–S sweep curves of the sheared suspensions were nearly superimposable regardless of heating. The movement of the position of a target in the sheared suspensions occurred at a larger strain than that in the unsheared suspensions. Shearing caused changes in the oscillatory dynamic moduli of storage (G′) and loss (Gʺ) as a function of strain: the unsheared suspensions behaved as solid-like viscoelastic matter, whereas the sheared suspensions gave similar magnitudes of the G′ and Gʺ values in the linear regions. Beyond the linear region, the Gʺ value showed strain overshoot regardless of the treatment. The steady state shear flow curves of the suspensions were compared with the Herschel–Bulkley equation; their fits were comparable and the calculated parameters in the equation were well correlated to the historical treatments of the suspensions.

Electrorheology of aniline oligomers

Aniline oligomers were prepared by the oxidation of aniline with p-benzoquinone in aqueous solutions of methanesulfonic acid (MSA) of various concentrations. Their molecular structures were assessed by Fourier transform infrared spectroscopy. The electrorheological (ER) behavior of their silicone oil suspensions under applied electric field has been investigated. Shear stress at a low shear rate, τ 0.9, was used as a criterion of the rigidity of internal structures created by the application of an electric field. It was established from the fitting of the dielectric spectra of the suspensions with the Havriliak–Negami model that dielectric relaxation strength, as a degree of polarization induced by an external field contributing to the enhanced ER effect, increases and relaxation time, i.e., the response of the particle to the application of the field, decreases when a higher molar concentration of MSA is used. The best values were observed for suspensions of the sample prepared in the presence of 0.5 M of MSA. This suspension creates stiff internal structures under an applied electric field strength of 2 kV mm−1 with τ 0.9 of nearly 50 Pa, which is even slightly of higher value than that obtained for standard polyaniline base ER suspension measured at the same conditions. The concentration of the MSA used in the preparation of oligomers seems to be a crucial factor influencing the conductivity, dielectric properties and, consequently, rheological behavior, and finally ER activity of their suspensions.

Electrorheology of polyaniline, carbonized polyaniline, and their core–shell composites

In the search for a new electrorheological system, silicone oil suspensions of polyaniline base, carbonized polyaniline base, and core–shell particles of carbonized polyaniline base coated with polyaniline base have been investigated. The conversion of the materials was followed by Raman spectroscopy. Although the apparent viscosity of the suspensions measured via rotational rheometer in the presence of an electric field was the same for all three samples, the core–shell structured particle-based electrorheological system showed considerably lower field-off viscosity, which resulted in higher electrorheological efficiency.

Electrorheology of aniline-oligomer suspensions under oscillatory shear

Preparation of the aniline oligomers by the oxidation of aniline with p-benzoquinone in the solutions of methanesulfonic acid (MSA) and the rheology of their suspensions in silicone oil are presented in this study. This synthesis provides particles of flake-like morphology and various conductivities depending on the molar concentration of MSA. Further, the electrorheological (ER) performance of the particles suspended in the silicone oil was measured as well as dielectric properties of suspensions. Finally, the effect of the temperature on the ER activity was investigated.

Synthesis and electrorheological effect of Cr doped TiO2 nanorods with nanocavities in silicone oil suspensions

Titanium dioxide (TiO2) nanorods with nanocavities doped with chromium (Cr) were synthesized by hydrothermal method. The morphology of prepared nanorods was determined by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX). The electrorheological (ER) behaviour of suspensions based on TiO2 was investigated under the steady shear, and the yield stress was chosen as a suitable tool for a comparison of ER performance. Some optimum in level of Cr doping of TiO2 was found.

Electrorheological behaviour under oscillatory shear of TiO2 rod-like particles prepared via microwave-assisted molten-salt synthesis

Titanium dioxide (TiO2) rod-like particles were synthesized by a simple and rapid microwave-assisted molten-salt method. The X-ray diffraction analysis and electron microscopy provided information on particle composition and morphology, respectively. It was found that during the synthesis process the crystalline phase of TiO2 transformed from anatase into rutile while the morphology changed from nanospheres into micrometer sized rod-like particles. The electrorheological (ER) properties were investigated via oscillatory shear tests. It was found that TiO2 rod-like particles based silicone oil suspensions exhibited higher ER activity than those of original anatase TiO2 nanoparticles probably due to side-by-side solid friction between particles as well as shorter time of their polarization. The changes in ER properties of rod-like particle based suspensions as a function of the applied electric field strength and particles weight fraction were also investigated.

Molecule-based electrorheological material with luminescence property

3+ among both of the complexes. The composition and structure are the dom- inant factors in improving the ER effect. The fluorescence intensity, fluorescence lifetime and emission quantum yield of the particle materials and their suspensions in silicone oil have been tested, and fine lumi- nescence performance has been detected. The material with ER activity and luminescence performance is a novel multifunctional material which would have wide application prospect.

New electrorheological fluid obtained from mercaptosilsesquioxane-modified silicate suspensions

Ormosil based on mercaptosilsesquioxane-modified silicate (SiO2/SSQ-SH) particle was prepared by sol–gel process involving a co-condensation of the hydrolyzed 3-mercaptopropyl-trimethoxysilane (MPTMS) and tetraetoxysilane (TEOS). The resulting material was characterized by 29Si solid nuclear magnetic resonance spectroscopy (29Si NMR), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FEG-SEM) and small angle X-ray scattering (SAXS). The (SiO2/SSQ-SH) particle presents a hierarchical structure, extending from micro to nanoscale and consisting of three structural levels. This SiO2/SSQ-SH particle was used for the first time as the dispersed phase in silicone oil suspension to develop a new electro-rheological fluid with a very good response under the action of electrical field from 1 to 4kV/mm, whose values are comparable to those exhibited by other conventional ER fluids, under the influence of electric field.

Electrorheological properties of polypyrrole-silica nanocomposite suspensions

The electrorheological (ER) and dielectric properties of PPy-silica nanocomposite suspensions in silicone oil were investigated. Various PPy-silica nanocomposite particles were synthesized by suspension polymerization in the presence of silica nanoparticles controlling the ratio of silica/pyrrole during the polymerization. The ER response and the particle conductivity increased with the increase in the silica/pyrrole ratio, indicating that the increased particle polarization plays a role in enhancing the ER response. The dielectric properties of PPy-silica nanocomposite particles and their suspensions support that the enhanced ER response with the increase in the silica/pyrrole ratio arises from the enhanced polarization, which originates from the increased particle polarization.

Spreading of a Suspension Drop on a Horizontal Surface

Experimental studies were performed on the contact line motion of a suspension of PS particles on a glass surface. The base liquids were silicone oil and glycerin. The particle size was in the range of 1-6 μm and the particle loading was 0.5-5 vol %. The drop shape was determined by using a drop image and its reflection and the drop outline was traced to the subpixel level. The Tanner-Voinov-Hoffman relation was valid for suspensions as well as for pure liquids. Silicone oil suspensions showed almost no noticeable change compared with the pure fluid. Glycerin suspensions showed an increase in contact line speed at low particle loading. The difference was due to the microstructure change at the contact line region, and the microstructure change was originated from the wetting characteristics of particles. Particle alignment occurred during the spreading stage for partially wetting particles. The contact line showed a stop-and-go fashioned motion due to surface irregularities. This result can be used as the boundary condition at the contact line in the numerical simulation of suspension spreading.