Silicone Oil Suspensions Research Articles

Gelatine-Coated Carbonyl Iron Particles and Their Utilization in Magnetorheological Suspensions.

This study demonstrates the formation of biocompatible magnetic particles into organized structures upon the application of an external magnetic field. The capability to create the structures was examined in silicone-oil suspensions and in a gelatine solution, which is commonly used as a blood plasma expander. Firstly, the carbonyl iron particles were successfully coated with gelatine, mixed with a liquid medium in order to form a magnetorheological suspension, and subsequently the possibility of controlling their rheological parameters via a magnetic field was observed using a rotational rheometer with an external magnetic cell. Scanning electron microscopy, infrared spectroscopy, and thermogravimetric analysis confirmed the successful coating process. The prepared magnetorheological suspensions exhibited a transition from pseudoplastic to Bingham behavior, which confirms their capability to create chain-like structures upon application of a magnetic field, which thus prevents the liquid medium from flowing. The observed dynamic yield stresses were calculated using Robertson–Stiff model, which fit the flow curves of the prepared magnetorheological suspensions well.

Electrorheology and shear dependent reversible gelation of elongated α-FeOOH suspensions

We study the effect of applying an external electric field (E) on the rheology and microstructure of α-FeOOH, length (L) = 488 ± 20 nm and an aspect ratio of (5 ± 0.8) – in – silicone oil suspensions (α-FeOOH/silicone oil). The α-FeOOH/silicone oil suspensions show Newtonian response up to α-FeOOH particle volume fraction of 0.039 when no E is applied. The suspensions exhibit τy ~ E2 and E1.5 scaling in the low and high E regimes respectively and the normalized τy versus E data of the suspensions collapses onto single master curve, irrespective of the particle loading and applied E. The solid-like behavior of the suspensions is also evident from the frequency-independent storage modulus, and the plateau in relaxation modulus with applied E. The optical microscopy reveals the E driven irreversible network formation of α-FeOOH particles, which does not relax to a uniform dispersion of α-FeOOH particles when the E is switched off. The suspensions demonstrate a reversible ER response once they are sheared at constant shear rate of 10 s−1.

The surfactant effect on electrorheological performance and colloidal stability.

The impact of two nonionic surfactants, namely Span 20 and Span 85, on the electrorheological response and colloidal stability of urea-coated barium titanyl oxalate (BTRU)/silicone oil suspensions is investigated. We quantitatively analyze the surfactant effect on modified ER performance through the measurements of yield stress and current density, as well as the tuned suspension stability through calculation of the Turbiscan stability index (TSI) and naked-eye observations of sedimentation phenomena. The surfactant effect on particle-oil interactions and agglomeration effects is examined by measuring the permeability of silicone oil when mixed with the Span surfactant and the cluster size of particles in dispersing medium, respectively. Our results indicate that with the presence of a Span surfactant, the yield stress of the suspension exhibits a local maximum at certain Span concentrations. We hypothesize that below the optimal Span concentration, the ER properties are enhanced by the increase of the electrostatic interaction between particles. Above the limiting concentration, the ER activity is weakened by the formation of a double-layer surfactant structure that generates a steric hindrance effect. We discover that the addition of the Span surfactant favors the improvement of the particle agglomeration phenomenon, thereby promoting colloidal stability of the suspension. Consequently, in the consideration of both ER properties and suspension stability, an optimal ER fluid with the addition of 0.4 wt% Span 85 is acquired with remarkable integrated ER properties.

Viscosity of Slag Suspensions with a Polar Liquid Matrix

Under the operating temperatures employed in steelmaking, most slags and fluxes often contain solids, such as undissolved CaO and its reaction products; thus, they are more viscous than their fully liquid states. However, few studies have considered the dielectric interactions of solid particles with the liquid matrix in such systems. In the present study, the viscosity of suspensions of dispersed particles consisting of polyethylene beads in a matrix of silicone oil or aqueous glycerol at room temperature was measured. Then, empirical models for estimating the viscosity based on the Einstein–Roscoe equation were proposed. Furthermore, the viscosity of suspensions of CaO and MgO particles dispersed in a matrix of CaO–Al2O3–SiO2–MgO slag at 1773 K was measured, and the feasibility of the proposed viscosity equations was investigated. As expected, the viscosities of the suspensions of polyethylene beads dispersed in silicone oil and glycerol increased with an increasing bead volume fraction. Under comparable measurement conditions, the viscosities of the glycerol suspensions were higher than those of the silicone oil suspensions. The proposed viscosity models based on the Einstein–Roscoe equation and the capillary number reproduced the viscosity of the silicone oil suspensions but underestimated that of the glycerol suspensions. The trend of increasing viscosity of the molten slag suspensions with dispersed CaO and MgO particles was similar to that of the room-temperature suspensions, exhibiting Bingham non-Newtonian behavior. The viscosity model composed with the results from the glycerol aqueous suspensions underestimated the slag viscosity, which can be attributed to the repulsive forces in the high-polarity liquid matrix.

Encapsulation of Activated Carbon into a Hollow-Type Spherical Bacterial Cellulose Gel and Its Indole-Adsorption Ability Aimed at Kidney Failure Treatment.

For reducing side effects and improvement of swallowing, we studied the encapsulation of activated carbon formulations with a hollow-type spherical bacterial cellulose (HSBC) gel using two kinds of encapsulating methods: Methods A and B. In Method A, the BC gelatinous membrane was biosynthesized using Komagataeibacter xylinus (K. xylinus) at the interface between the silicone oil and cell suspension containing activated carbon. In Method B, the bacterial cellulose (BC) gelatinous membrane was formed at the interface between the cell suspension attached to the alginate gel containing activated carbon and the silicone oil. After the BC gelatinous membrane was biosynthesized by K. xylnus, alginate gel was removed by soaking in a phosphate buffer. The activated carbon encapsulated these methods could neither pass through the BC gelatinous membrane of the HSBC gel nor leak from the interior cavity of the HSBC gel. The adsorption ability was evaluated using indole, which is a precursor of the uremic causative agent. From curve-fitting, the adsorption process followed the pseudo-first-order and intra-particle diffusion models, and the diffusion of the indole molecules at the surface of the encapsulated activated carbon within the HSBC gel was dominant at the initial stage of adsorption. It was observed that the adsorption of the encapsulated activated carbon by the intraparticle diffusion process became dominant with longer adsorption times.

Tuning the thermal conductivity of nanoparticle suspensions by electric field

Active thermal management is essential for the operation of modern technologies like electronic circuits and spacecraft systems to deal with the complex control and conversion of thermal energy. One basic requirement for the materials is its tunable and reversible thermal properties. Here, we try to provide a systematic investigation of the thermal smart materials composed of low-dimensional solid particles suspended in liquid media, whose structures and properties can be tuned by external field. A two-step theoretical model, which takes into account the effects from particle aggregation and orientational variation, was proposed and obtained reasonable agreement with both literature and our own experimental results. Graphene nanosheets/Mg-Al layered double hydroxides (GNS/LDH) were fabricated and their silicone oil suspension shows reversible thermal conductivity switching under DC electric field due to the formation/break-up of chain-like structures with a maximum switching ratio around 1.35×. This study reveals the underlying mechanism of thermal conductivity enhancement in nanoparticle suspensions, and provides a preliminary example to design and fabricate responsive thermal materials for the next generation technologies.

First MnO2-based electrorheological fluids: high response at low filler concentration

Nanoparticles of MnO2 with different shapes (needle-like α-MnO2 and spherical δ-MnO2) were proposed as promising fillers for electrorheological fluids (ERFs). A thorough study of the dielectric properties of α-MnO2 and δ-MnO2 suspensions in silicone oil enabled estimation of the values of their dielectric permittivity and dielectric relaxation times. The study of MnO2-filled materials with various filler contents, and under various electric field strengths, in shear and uniaxial tensile and compressive stress regimes, revealed that needle-like α-MnO2 nanoparticles, in comparison with spherical δ-MnO2 particles, lead to better mechanical properties of the fluids. The most intriguing property of MnO2-based electrorheological fluids is their high electrorheological response at low filler content: ERF containing only 4.5 vol.% of α-MnO2 in silicone oil demonstrated a 18 kPa tensile strength in a 5 kV electric field.

Encapsulation of Micro- and Milli-Sized Particles with a Hollow-Type Spherical Bacterial Cellulose Gel via Particle-Preloaded Droplet Cultivation.

A hollow-type spherical bacterial cellulose (HSBC) gel prepared using conventional methods cannot load particles larger than the pore size of the cellulose nanofiber network of bacterial cellulose (BC) gelatinous membranes. In this study, we prepared a HSBC gel encapsulating target substances larger than the pore size of the BC gelatinous membranes using two encapsulating methods. The first method involved producing the BC gelatinous membrane on the surface of the core that was a spherical alginate gel with a diameter of 2 to 3 mm containing the target substances. With this method, the BC gelatinous membrane was biosynthesized using Gluconacetobacter xylinus at the interface between the cell suspension attached onto the alginate gel and the silicone oil. The second method involved producing the BC gel membrane on the interface between the silicone oil and cell suspension, as well as the spherical alginate gel with a diameter of about 1 mm containing target substances. After the BC gelatinous membrane was biosynthesized, an alginate gel was dissolved in a phosphate buffer to prepare an HSBC gel with the target substances. These encapsulated substances could neither pass through the BC gelatinous membrane of the HSBC gel nor leak from the interior space of the HSBC gel. These results suggest that the HSBC gel had a molecular sieving function. The HSBC gel walls prepared using these methods were observed to be uniform and would be useful for encapsulating bioactive molecules, such as immobilized enzymes in HSBC gel, which is expected to be used as a drug carrier.

Surfactant-Switched Positive/Negative Electrorheological Effect in Tungsten Oxide Suspensions.

The electrorheological (ER) effect was experimentally observed in dielectric suspensions containing tungsten oxide (WO3) modified with surfactant molecules (sodium dodecyl sulfate (SDS) and dodecylamine (DDA)) in electric fields up to several kilovolts per millimeter. The dielectric properties of WO3 suspensions in silicone oil were analyzed, depending on the frequency of the electric field, in the range from 25 to 106 Hz. Unmodified WO3 suspensions, as well as suspensions modified with sodium dodecyl sulfate, were shown to exhibit a positive electrorheological effect, whereas suspensions modified with dodecylamine demonstrated a negative electrorheological effect. The quantitative characteristics of the negative electrorheological effect in the strain–compression and shear regimes were obtained for the first time. Visualization experiments were performed to see the chain structures formed by WO3 particles modified with sodium dodecyl sulfate, as well as for dynamic electroconvection in electrorheological fluids containing WO3 modified with dodecylamine. The negative electrorheological effect was shown to be associated with the processes of phase separation in the electric field, which led to a multiplicative effect and a strong electroconvection of the suspension at field strengths above 1 kV/mm.

Electrorheological behaviour of suspensions in silicone oil of doped polyaniline nanostructures containing carbon nanoparticles

Electrorheological fluids have been paying a lot of attention due to their potential use in active control of various devices in mechanics, biomedicine or robotics. An electrorheological fluid consisting of polarizable particles dispersed in a non-conducting liquid is considered to be one of the most interesting and important smart fluids. This work presents the effect of the dopant, camphorsulphonic acid or citric acid, on the electrorheological behaviour of suspensions of doped polyaniline nanostructures dispersed in silicone oil, revealing its key role. The influence of carbon nanoparticle concentration has also been studied for these dispersions. All the samples showed an electrorheological effect, which increased with electric field and nanostructure concentration and decreased with silicone oil viscosity. However, the magnitude of this effect was strongly influenced not only by carbon nanoparticle concentration but also by the dopant material. The electrorheological effect was much lower with a higher carbon nanoparticle concentration and doped with citric acid. The latter is probably due to the different acidities of the dopants that lead to a different conductivity of polyaniline nanostructures. Furthermore, the effect of the carbon nanoparticles could be related to its charge trapping mechanism, while the charge transfer through the polymeric backbone occurs by hopping. Polyaniline/camphorsulphonic acid composite nanostructures dispersed in silicone oil exhibited the highest electrorheological activity, higher than three decades increase in apparent viscosity for low shear rates and high electric fields, showing their potential application as electrorheological smart materials.

Impact of corrosion process of carbonyl iron particles on magnetorheological behavior of their suspensions

The study investigates an influence of carbonyl iron (CI) particles’ corrosion on magnetorheological performance of their silicone-oil suspensions. Carbonyl iron particles were oxidized thermally at 500°C in the air or chemically in 0.05 HCl solution and the as-treated particles were subsequently used as a dispersed phase in magnetorheological suspensions. Corrosive layer on surface of oxidized particles was investigated using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Obtained rheological data was treated with Robertson–Stiff (R–S) model to determine yield stress values and in order to find the yield stress values of prepared magnetorheological (MR) suspensions at saturation level a mathematical model was used. The suspensions based on oxidized particles showed lower values of the yield stress, which was significantly manifested at higher magnetic field intensities due to lower saturation magnetization of the particles.

The electrorheological performance of polyaniline-based hybrid particles suspensions in silicone oil: influence of the dispersing medium viscosity

The potential of electrorheological (ER) suspensions based on polarizable particles in simple liquids relies on the particles arrangements which turn their quasi Newtonian behavior into gel-like. However, minor attention has been paid to the effect provoked by the liquid viscosity on the ease of orientation and assembly of the particles. With this aim, a study on the ER behavior, at 25 °C, of 1 wt% suspensions of polyaniline (PANI)-based hybrid particles (—graphene or —tungstene oxide) in silicone oil with varying viscosities (20, 50 and 100 cSt) was carried out. The electric field effect was higher for the PANI-graphene particles suspension in the less viscous silicone oil. However, two drawbacks were observed: (a) higher leakage current flows; and (b) reduced reversibility upon the electric field was turned off. The use of silicone oil with higher viscosity solved these issues.

Electrorheological properties of algae dispersed suspension: New application of harmful algae

The algae has been considered as a bane which should be removed due to its harmful influences on human health and aquatic ecosystems. Recently, various applications of the algae have been studied as a new alternative method instead of its sequestration, to treat vast algae blooms. Herein, algae particles dispersed suspensions have been investigated as a promising new application to electrorheological fluids without any further processing, such as chemical modification, extraction and carbonation. Algae particles dispersed silicone-oil suspensions exhibited good electrorheological properties under DC electric fields, and their electrorheological performances were enhanced with increase of electric fields. The alignment of algae particles along DC electric fields in the suspension, that inhibits the suspension flow by the drag of the dangling alignments and consequently increases the viscosity of the suspension, was observed under the electric fields. The ER properties of algae particles dispersed suspensions were same with (or similar to) those of cellulose phosphate dispersed suspension (yield stress: ca. 400 Pa at 3 kV/mm; polarizability, Δε: ca. 0.35) owing to the phosphate groups in the algae particles. Our research has demonstrated that the electrorheolgical fluids is very promising for the ecofriendly application of the mass-producing algae particles.

Surface-initiated atom transfer radical polymerization from graphene oxide: A way towards fine tuning of electric conductivity and electro-responsive capabilities

Presence of the tertiary amine in the reaction mixture during surface-initiated atom transfer radical polymerization (SI-ATRP) possess dual functionality, reduction of the graphene oxide (GO) and proceed the poly(methyl methacrylate) (PMMA) chain growth simultaneously. In the certain ratio between the ligand and GO, the slight reduction of the GO can be achieved and thus fine tuning of the conductivity is possible. Such benefits were utilized in the development of the novel dispersed phase based on GO-PMMA hybrid particles and their silicone oil suspensions for which their electro-responsive capabilities were investigated. This approach provides system which is very effective at very low particles concentrations (10 wt%) and serving the shear stresses from 5 to 95 Pa depending on the conductivity of particles and applied external electric field.

Molybdenum and tungsten disulfides surface-modified with a conducting polymer, polyaniline, for application in electrorheology

Molybdenum and tungsten sulfides are semiconducting materials with flake-like morphology. Their applicability in electrorheological suspensions was enabled by the coating with a conducting polymer, polyaniline, after its conversion to non-conducting polyaniline base. For instance, the conductivity of tungsten sulfide, 0.056Scm−1, increased to 0.98Scm−1 after coating with polyaniline, and was conveniently reduced to 6.3×10−6Scm−1 after conversion to polyaniline base. Such approach reduces the potential current drifts in electrorheological suspensions and allows for the application of sulfides in electrorheology. The optical microscopy demonstrated the formation of particle chains in silicone-oil suspensions after application of electric field. The electrorheological performance was assessed by the measurement of viscosity on the shear rate in the absence and in the presence of electric field and it is discussed on the bases of dielectric spectra.

Tunable electrorheological performance of silicone oil suspensions based on controllably reduced graphene oxide by surface initiated atom transfer radical polymerization of poly(glycidyl methacrylate)

This article is focused on the controllable reduction of the graphene oxide (GO) particles as a simultaneous process during surface initiated atom transfer radical polymerization (SI-ATRP) providing hybrid particles with tailored conductivity and substantial polymer shell on the particles tunable by SI-ATRP conditions. The main advantage of such approach is that both the compatibility improvement, due to the polymer layer, and conductivity tuning, due to partial GO reduction, were simply achieved in single-step reaction providing electrorheological (ER) system with enhanced performance in comparison to either neat GO or similar non-covalently bonded GO-polymer hybrids. The presence of the poly(glycidyl methacrylate) (PGMA) on the surface of GO was investigated using FTIR spectrometry, transmission electron microscopy and thermogravimetric analysis and their chain length (Mw) and polydispersity index (PDI) were determined by 1H NMR and GPC, respectively. Two different GO-PGMA particle systems varied in Mw and PDI and also in electrical conductivities were prepared and their electro-responsive capabilities were investigated. The reduction of GO particles was confirmed by Raman shift as well as conductivity measurements. Electrorheological (ER) performance was investigated at various electric field strengths and repeatability of the phenomenon was confirmed by 10 on/off field cycles. Finally, with the help of dielectric measurements of GO-PGMA based ER suspensions, fitted by Havriliak–Negami model, the relaxation processes were properly investigated and the results were correlated with those obtained from electrorheological measurements.

Ionic liquid-based organically modified silica for the development of new electrorheological fluids

This work describes the preparation of novel electrorheological (ER) fluids consisted of organically modified silica particles with imidazolium-based ionic liquid (IL-ORMOSIL) suspended in a silicone oil. The IL-ORMOSIL was prepared by hydrolysis/co-condensation of tetraethoxy silane (TEOS) in the presence of different concentration of 1-(3-trimethoxysilylpropyl)-3-methylimidazolium chloride (IL-TMOS), using the one-pot sol-gel process. IL-ORMOSIL particles with controlled morphology were obtained, as indicated by transmission electronic microscopy (TEM). The presence of the silylated ionic liquid covalently attached to the silica particles was confirmed by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The effect of the amount of imidazolium-based ionic liquid immobilized on the spherical silica particles on the electrorheological (ER) behavior of the corresponding suspensions in silicone oil was investigated. A significant ER effect was observed for the fluid containing silica modified with around 10%wt. of IL-TMOS. In fact, a very good, extremely rapid and reversible response under the action of an electric field at intensity to 4kV/mm was achieved, with shear stress value as high as 2200Pa. The dielectric properties were also evaluated to explain the ER response of these IL-ORMOSIL particles

Influence of electric field and shear on the rheology of fumed alumina in silicone oil suspensions

We investigate the effect of shear and electric field (E) on the rheology of fumed alumina (Al2O3) − in − silicone oil suspensions (Al2O3/silicone oil) at varying Al2O3 nanoparticle loadings of 0.5wt%–15wt%. 0.5wt% and 2.5wt% Al2O3/silicone oil suspensions behave as Newtonian fluids and form gel − like suspensions at a nanoparticle loading of 10wt% and above; attributed to the formation of a particulate network of fumed Al2O3 nanoparticles. Transient step − down experiments with 5wt% and 15wt% Al2O3/silicone oil suspensions indicate shear thinning and thixotropy. We also show that the dynamic rheology of gel − like 15wt% Al2O3/silicone oil suspensions is extremely sensitive to the preshearing protocols. Depending on the preshear, partial or complete breakdown of the network structure in 15wt% Al2O3/silicone oil suspensions is observed. Once the network structure breaks, the structural recovery doesn’t ensue at rest after the cessation of shear. On application of E, Al2O3/silicone oil suspensions with 0.5wt%–5wt% Al2O3 nanoparticle loading exhibit diverging low shear viscosity, frequency independent G′ along with the presence of a yield stress. The electrorheological response of 5wt% Al2O3/silicone oil suspensions is independent of the preshearing protocols at an applied E=1kV/mm. Furthermore, the shear rheology with applied E does not scale with γ˙E2, instead linear and sub-linear scaling with applied E is observed.

Photo-effects on the viscosity of titania nanoparticle suspensions in conducting and insulating medium

The effect of illumination on the viscosity of titania suspensions in silicone oil (insulating medium) and an aqueous buffer (conducting medium) was investigated. Commercially available P25 anatase titania was suspended at a volume fraction of 0.5%. A 12.3% increase in viscosity was observed when silicone oil suspension was used as the medium, while a 2.47% decrease in viscosity was observed for the aqueous buffer suspension after exposure to UV-vis irradiation. The capability of the suspension medium to scavenge photoinduced charges results in the observed photorheological effects. The results presented here demonstrate a new method for influencing the rheological properties of nanoparticle suspensions.

Carbonyl iron coated with a sulfobetaine moiety as a biocompatible system and the magnetorheological performance of its silicone oil suspensions

In this study, surface modification of carbonyl iron (CI) particles with sulfobetaine moieties (SBE) was performed by the silanization of activated CI to form stable CI–SBE particles.