Steady Shear Mode Research Articles

An experimental study on thermo-field rheological properties of lithium-based magnetorheological grease

In this paper, the effects of temperature and magnetic field strength on the dynamic rheological properties of magnetorheological grease are mainly studied. Firstly, the magnetorheological grease of carbonyl iron powder with a weight percentage of 70% was prepared by a mechanical stirrer. In steady state shear mode, the apparent viscosity and shear stress of lithium-based greases and magnetorheological greases at different magnetic field strengths and temperatures are measured. It is found that both apparent viscosity and shear stress decreased correspondingly with increasing temperature. Compared with the zero-field test results, the apparent viscosity of magnetorheological grease after applying a magnetic field is less affected by temperature. In addition, the Bingham model is combined with the Arrhenius model to derive mathematical formulas for shear yield stress and viscosity including temperature and magnetic field strength. Then, the dynamic rheological response behavior of magnetorheological grease at different temperatures is also tested, and the results showed that magnetorheological grease has viscoelastic properties. Finally, the stress-strain response parameter model of magnetorheological grease at different temperatures is established, and the parameters of the model are optimized by fish swarm algorithm. It is found that the model can describe the dynamic hysteresis response of magnetorheological grease very well.

The Rheological Studies on Poly(vinyl) Alcohol-Based Hydrogel Magnetorheological Plastomer.

The freezing–thawing method has been commonly used in the preparation of polyvinyl alcohol hydrogel magnetorheological plastomer (PVA HMRP). However, this method is complex and time consuming as it requires high energy consumption and precise temperature control. In this study, PVA HMRP was prepared using a chemically crosslinked method, where borax is used as crosslinking agent capable of changing the rheological properties of the material. Three samples of PVA HMRP with various contents of carbonyl iron particles (CIPs) (50, 60, and 70 wt.%) were used to investigate their rheological properties in both steady shear and dynamic oscillation modes. Results showed the occurrence of shear thickening behaviour at low shear rate (γ > 1 s−1), where the viscosity increased with the increased of shear rate. Moreover, the storage modulus of the samples also increased increasing the oscillation frequency from 0.1 to 100 Hz. Interestingly, the samples with 50, 60 70 wt.% of CIPs produced large relative magnetorheological (MR) effects at 4916%, 6165%, and 10,794%, respectively. Therefore, the inclusion of borax to the PVA HMRP can offer solutions for a wide range of applications, especially in artificial muscle, soft actuators, and biomedical sensors.

Poly(2,5-dimethoxyaniline) coated polystyrene microspheres and their electrorheological characteristics

We synthesized core–shell type spherical semiconducting poly(2,5-dimethoxyaniline) (PDMA)-coated polystyrene (PS) (PS/PDMA) particles with uniform size and investigated their electrorheological (ER) response. Using monodisperse PS microspheres initially synthesized by dispersion polymerization, 2,5-dimethoxyaniline monomer was pre-adsorbed onto the PS surface via π–π stacking interaction, and then PDMA was synthesized by oxidative polymerization. Morphology of the synthesized PS/PDMA particles was observed by both scanning electron microscopy and transmission electron microscopy, while their chemical compound was confirmed by Fourier transform infrared spectroscopy. The PS/PDMA microspheres were suspended in silicone oil and their ER properties were studied using a rotational rheometer from both steady shear and oscillatory test modes. Flow curves were observed to be fitted well with the Bingham fluid equation, while all three differently measured yield stresses showed similar electric field dependence. Furthermore, dielectric analysis confirmed the degree of relaxation time and polarizability related to the ER behaviors of the PS/PDMA particle-based ER fluid. PS/PDMA particles with several advantages such as easy conductivity control through a doping and a de-doping process, their spherical shape and controllable size are expected to be of great help in their multiple applications in both ER fluids and colloidal science.

Rheological analysis of particle aggregation in a colloidal suspension of carbon black particles

We examine scaling theories to estimate microstructural parameters of fractal aggregates in a colloidal suspension. The scaling theories are based on fractal theories and rheological properties of the colloidal suspension. Rheological measurement in oscillatory and steady shear modes is performed for colloidal suspensions of 56 nm carbon black particles in Newtonian ethylene glycol at the particle volume fractions φ ranging from 0.005 to 0.05. Elastic modulus G’ of the colloidal suspension at φ = 0.02-0.05 in the state of colloidal gel is used to estimate fractal dimension df of the aggregates. Steady-shear measurement gives yield stress τy as a function of φ. Shear dependence of the aggregate radius R is given by a power-law scaling, i.e., R∝S−m, where S is the shear rate. The power-law exponent m is estimated from df and a scaling relation between τy and φ. The estimation gives df = 2.14 and m = 0.33. The parameters df and m which can be determined by either direct measurement or theoretical calculation are used to establish a microrheological model for predicting shear viscosity of aggregated suspension as a function of φ and S. Both the concentration dependence and the shear dependence of aggregates are combined to obtain an expression for the shear viscosity. Hydrodynamic interaction effect among the aggregates is roughly considered in calculating average shear stress on the aggregate. It is found that this consideration critically contributes to behavior similarity with experimental result. It is shown that the predictions by the model reasonably agree with the experimental result.

Effects of wall slip on the rheological measurement and extrusion die design of a filled rubber compound

We investigate the rheological properties of a filler-reinforced rubber compound using a rotorless shear rheometer specially designed for rubber and a rotational rheometer with parallel-plate geometry. Our aim is to evaluate the effects of wall slip on both the oscillatory and steady shear modes of the rotational rheometer. The rheological measurements show that the slip generally does not affect the oscillatory shear but does exist in the steady shear flow and tends to make the measured shear viscosity lower than the true value. Besides, we extend the investigation into engineering applications. The extrusion die for a given extrudate profile is obtained using a finite-element model in which the wall slip is considered as a boundary condition. To validate the die design, an extrusion experiment is carried out and the results confirm that, for filled elastomers, it is necessary to consider the effect of wall slip in the extrusion die design.

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.

Normal force for static and steady shear mode in magnetorheological fluid

This paper presents the normal force phenomena for static and steady shear mode in magnetorheological (MR) fluid. The results of the study show that, in the static mode, with the magnetic flux density increasing, the normal force will increase until the maximum, and then reduce to a steady value, and during the increasing stage, it can be expressed as FN=4667*B2.48 approximately; however, in the steady shear mode, only when the magnetic flux density achieves a certain value, the normal force phenomena will be observed clearly, and with the increasing of magnetic field, the normal force reaches the maximum, and then also decreases to a steady value. Besides, by defining the time parameters of dynamic response, the dynamic response of normal force is studied. If the shear plate is stationary, from the magnetic field on to a stable normal force produced, the response time is about 25.11ms.

Effect of interface on mechanical properties and biodegradation of PCL HAp supramolecular nano-composites

This research explores the correlation between the structural properties of supramolecular biocomposites and their mechanical strength. Hybrid biocomposites composed of surface-modified hydroxyapatite nano-particles and supramolecular polycaprolactone (SP PCL), were prepared at different compositions, and their mechanical, thermal and viscoelastic properties as well as biodegradability, biocompatibility and cytotoxicity were evaluated in vitro. The results were compared with those for SP PCL/naked hydroxyapatite nano-composites. We show that surface modification of hydroxyapatite nanoparticles resulted in outstanding improvement of tensile strength and modulus up to 3.6 and 2.2-fold, respectively. At above 10 wt% HAp and 20 wt% HApUPy, heterogeneous nano-composites with inferior mechanical properties were obtained. Based on rheological (in steady shear mode) and small/wide angle X-ray scattering measurements, unusual improved mechanical properties were ascribed to the formation of supramolecular clusters around nanoparticles. In-vitro degradation of the supramolecular nano-composites was also studied to investigate the overall product biodegradation as well as toxicity of the degradation product(s).

Preparation and electrorheological characteristics of uniform core/shell structural particles with different polar molecules shells

The core/shell structural dielectric particles are applied widely in the electrorheological (ER) fluids. In this work, we rationally designed and constructed two kinds of core/shell structured SiO2-based particles with TiO2 and hydroxyl titanium oxalate (TOC) as shell, respectively. The obtained core/shell structural SiO2/TiO2 and SiO2/TOC particles were well dispersed spherical nanoparticles with ideal morphology and a narrow size distribution. Under DC electric fields, the ER effect of the two kinds of core/shell particles dispersed in electrically insulating oil was examined and compared by steady shear flow and dynamic shear modes. It was found that the SiO2/TOC ER fluid showed a stronger ER effect compared to the SiO2/TiO2 ER fluid. The static yield stress of the SiO2/TOC ER fluid was up to 45kPa at 5kV/mm, which was twice of the SiO2/TiO2 ER fluid and 9 times of the SiO2 ER fluid. On the other hand, the zero field viscosity of the SiO2/TOC ER fluid was obviously lower than that of the SiO2/TiO2 ER fluid. Therefore, the ER efficiency of the SiO2/TOC ER fluid was much higher than that of SiO2/TiO2 ER fluid at the same electric field.

Synthesis, characterization and properties of a castor oil modified biodegradable poly(ester amide) resin

A biodegradable poly(ester amide) resin was synthesized from N,N-bis(2-hydroxy ethyl) fatty amide of castor oil with maleic anhydride, phthalic anhydride and isophthalic acid (100:30:35:35 mole ratio) by the polycondensation process. The fatty amide of the oil was obtained for the first time with 95% yield. The chemical structure of the synthesized resin was characterized by spectroscopic techniques like FTIR, 1H NMR and 13C NMR. Various physical properties such as acid value, saponification value, iodine value, specific gravity and viscosity of the resin were also determined. Further the rheological behavior, studied in the steady shear mode showed shear thinning behavior of the resin. The epoxy cured poly(ester amide) thermoset using poly(amido amine) hardener exhibited better properties than with the cycloaliphatic amine hardener cured system. TGA studies also revealed higher thermal stability of the former system than the latter. In vitro-biodegradation study of the poly(ester amide) thermoset using Pseudomonas aeruginosa and Bacillus subtilus bacteria revealed superior biodegradability of the thermoset using the former bacterial strain. Excellent chemical resistance against various chemical media including alkali was observed for epoxy-poly(amido amine) cured poly(ester amide) resin over epoxy-cycloaliphatic amine one. The epoxy-poly(amido amine) cured poly(ester amide) thermoset thus has the potential to be used as surface coating material.

Multi-Walled Carbon Nanotube/Biodegradable Poly(butyleneadipate-co-butyleneterephthalate) Nanocomposites and Their Physical Characteristics

Biodegradable poly(butylene adipate-co-terephthlate) (PBAT) nanocomposites with multi-wall carbon nanotube (MWNT) were prepared by using a laboratory-scale twin-screw extruder. The effects of the MWNT-reinforcements on their thermal and mechanical properties were examined by various techniques such as thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and a universal testing machine (UTM). In addition, the morphology of the as-synthesized PBAT/MWNT nanocomposites was investigated by both scanning electron microscope (SEM) and transmission electron microscope (TEM). To compare the physical characteristics of the polymer nanocomposites with those of the pure polymer, samples with various ratios of MWNT in the PBAT matrix were prepared. Rheological properties of the PBAT/MWNT nanocomposites were investigated using a rotational rheometer in a steady shear mode. The steady shear viscosity increased with the MWNT loading, and the shear thinning viscosity data were fitted well with the power law model. Furthermore, UTM, DMA and TGA tests showed that both mechanical and thermal properties were improved by adding MWNT. In particular, the tensile strength and thermal stability of biopolymer/MWNT nanocomposite increased with increasing MWNT contents. These results indicated that filler-polymer interaction is important and the role of the MWNT as a reinforcement in the nanocomposites was evident.

Rheological Study of Vegetable Oil Based Hyperbranched Polyurethane/Multi-Walled Carbon Nanotube Nanocomposites

Hyperbranched polyurethanes [HBPUs] and vegetable oil based polymer nanocomposites have been drawing an imperative attention for their plentiful advantages across a spectrum of potential applications. This study divulges the rheological behaviors of Mesua ferrea L. seed oil modified HBPU/multiwall carbon nanotube [MWCNT] nanocomposites prepared by in-situ technique. Rheological phase transition behavior was studied at 120°C in the steady shear and oscillation mode. The nanocomposites showed shear thinning behavior in both the modes. The rheological characteristics were dependent on the loading of the nanotube as confirmed from this study. The storage and loss moduli values were higher than the pure HBPU and they showed improved viscosity by nanocomposite formation. The nanocomposites revealed a pseudo–solid-like behavior at relatively low frequencies. The effects of temperature on storage and loss modulus have also been explored. The temperature dependence complex viscosity further described the ease of processibility. It has been tried to establish a structural property relationship of the systems from rheological study.

The electrorheological effect and dielectric properties of suspensions containing polyaniline@titania nanocable-like particles

The core/shell structured particle is one of the most promising electrorheological materials. In this paper, we prepared two kinds of core/sheath structured polyaniline@titania nanocable-like particles with conducting cores and non-conducting cores for use as new nanofiber-based ER fluids. The morphology and structure of the nanocables were characterized by scanning electron microscopy, transmission electron microscopy, line profiles of element content, and Fourier transform infrared spectra. Under DC electric fields, the ER effect of the unique cable-like nano-architectures dispersed in electrically insulating oil was examined and compared by steady shear flow and dynamic oscillatory shear modes. It was found that the two nanocable suspensions showed distinctly different ER responses, which depended on the conductivity of the core. The suspension containing nanocables with a conducting polyaniline core exhibited high static yield stress but unstable flow curves and abrupt rupture behavior when the stress was beyond the yield point, while the suspension containing nanocables with a non-conducting polyaniline core exhibited stable flow curves and gradual rupture behavior. The dielectric spectra measurements indicated that there was a significant difference in the polarization response between the two nanocable suspensions, which could produce the different rheological properties.

Nano-sized Fe soft-magnetic particle and its magnetorheology

As a new magnetoresponsive magnetorheological (MR) material under an applied magnetic field, magnetic Fe nanoparticles were synthesized from a simple process of thermal decomposition of pentacarbonyl iron using oleyl amine and kerosene at 150 °C. Morphology of the fabricated Fe nanoparticle was examined using both scanning electron microscopy and transmission electron microscopy. MR characteristics of the nano-sized magnetic particle-based MR fluid dispersed in non-magnetic carrier fluid was investigated using a rotational rheometer under different external magnetic field strengths, focusing on their flow behaviors at a steady shear mode and yield stress. Flow curve was also found to be fitted well with the Casson equation.

Effect of Magnetic Nanoparticle Additive on Characteristics of Magnetorheological Fluid

Magnetorheological (MR) fluids, suspension of magnetic pure carbonyl iron (CI) in non magnetic carrier, were prepared with and without magnetic CI nanoparticle additive in this study. Initially, the magnetic CI nanoparticle additive was synthesized in a rather simple process of decomposition of penta carbonyl iron (Fe(CO)5) using oleyl amine and kerosene. Magnetic property and morphology of the synthesized magnetic CI nanoparticles were confirmed via vibration sample magnetometer (VSM) and transmission electron microscopy (TEM), respectively. MR fluids, prepared as a mixture of pure CI and CI nanoparticle additive of different weight ratio in carrier fluid, was investigated under different external magnetic field strengths via a rotational rheometer. Sedimentation of the MR fluid was characterized by an optical analyzer, Turbiscan. Their flow behaviors at a steady shear mode were examined with and without magnetic CI nanoparticle additive under magnetic field strength. The MR fluids with magnetic CI nanoparticles added demonstrated slightly higher yield behaviors, suggesting that pure CI and CI nanoparticle additive were being oriented in the magnetic field direction under an applied magnetic field and with much strengthened structure.

Fabrication and magnetorheological property of core/shell structured magnetic composite particle encapsulated with cross-linked poly(methyl methacrylate)

Hybrid magnetic particle of carbonyl iron (CI) microsphere and cross-linked poly(methyl methacrylate) (PMMA) with core/shell structure was prepared to be adopted as a dispersed particle for a magnetorheological (MR) fluid. The magnetic hybrid composite microsphere was synthesized via a dispersion polymerization in the presence of CI, in which the PMMA was cross-linked using ethylene glycol dimethacrylate during polymerization for its enhancement in both chemical resistance and surface hardness. Magnetic property and morphology of the produced hybrid particles were examined via a vibrating sample magnetometer and scanning electron microscopy, respectively. The hybrid magnetic microsphere based MR fluids were then investigated under different external magnetic field strengths via a rotational rheometer. Their flow behaviors showing typical MR characteristics at a steady shear mode along with shear viscosity were examined under applied external magnetic field strength.

Magnetic carbonyl iron nanoparticle based magnetorheological suspension and its characteristics

Magnetic nano-sized carbonyl iron (CI) particle was prepared and adopted as an additive for micron-sized CI based magnetorheological (MR) fluid, in which the magnetic nanoparticle was fabricated via decomposition of pentacarbonyl iron (Fe(CO) 5). Magnetic property and morphology of the nanoparticle were confirmed via vibration sample magnetometer (VSM) and transmission electron microscopy (TEM), respectively. MR fluids, consisting of micron-sized CI and carrier fluid, were investigated under different external magnetic field strengths via a rotational rheometer. Their flow behaviors at a steady shear mode were examined with and without a nano-sized magnetic additive under magnetic field strength. The MR fluid with magnetic CI nanoparticle added demonstrated slightly higher yield behaviors, suggesting that micron-sized CI and magnetic CI nanoparticle particle were being oriented in magnetic field direction under applied magnetic field and with strengthened structure.

Gelation Kinetics and Performance Evaluation of an Organically Crosslinked Gel at High Temperature and Pressure

Summary Organically crosslinked gels have been used to control water production in high temperature applications. These chemical systems are based on the crosslinking of a polyacrylamide-based polymer/copolymer with an organic crosslinker. Polyethyleneimine (PEI) has been used as an organic crosslinker for polyacrylamide-based copolymers to provide thermally stable gels. Literature reported that PEI can form aqueous gels with polyacrylamide (PAM) at room temperature. In this paper, we show for the first time the possibility of crosslinking polyacrylamide with PEI at temperatures up to 140°C (285°F) and pressures up to 30 bars (435 psi). This paper reports data both in bulk and in porous media. The gelation time of the PAM crosslinked with PEI at high temperatures up to 140°C (285°F) and pressures up to 435 psi (30 bars) was measured. The effects of polymer concentration, crosslinker concentration, temperature, salinity, initial pH value, and the initial degree of hydrolysis of the polymer on the gelation time were examined in detail. All measurements were conducted in the steady shear mode. 13C Nuclear Magnetic Resonance Spectroscopy (13C NMR) was used to relate the gelation time to changes in the structure of the polymer and hence explain the variation in the gelation time in terms of the gelling system chemistry. In bulk, thermally stable gels were obtained by crosslinking PAM with PEI at 130°C (266°F) for at least 8 weeks. The performance of the PAM/PEI system in sandstone cores at a temperature of 90°C (194°F) and pressure drops of 68.95 bars (1,000 psi) was examined. The system was found to be stable for 3 weeks, where the permeability was reduced by a factor of 100%.

Rheology of a thermoplastic paste through the mushy state transition

The rheology of a highly filled thermoplastic paste employed in a novel continuous casting process was investigated across the melt-mushy zone temperature transition. The paste comprises of an ultrafine (or nano-particulate) zinc oxide powder ( d 1 , 0 = 85 nm , 50 vol%) and a continuous phase consisting of a blend of organic waxes with an onset of solidification around 54 ∘ C . Data were collected over nine decades of shear rate, using controlled strain and controlled stress devices, steady shear and oscillatory modes, rotational rheometry, and capillary rheometry using the multi-pass technique. The melt rheology could be described using a Carreau-type constitutive model, with strong evidence of a low shear rate viscosity plateau and a possible high shear rate viscosity plateau, with a transition between the two described by a highly shear-thinning power-law region. Nearer the solidification temperature the material exhibited strong pseudo-plastic behaviour, and capillary flow appears to be determined by pressure-dependent slip behaviour.

Preparation and Rheological Characteristics of Ethylene‐Vinyl Acetate Copolymer/Organoclay Nanocomposites

Ethylene‐vinyl acetate copolymer (EVA) with 40 wt.% vinyl acetate content (EVA40)/organoclay nanocomposites were prepared using a melt intercalation method with several different clay concentrations (2.5, 5.0, 7.5, and 10.0 wt.%). X‐ray diffraction confirmed the formation of exfoliated nanocomposite in all cases with disappearance of the characteristic peak corresponding to the d‐spacing of the pristine organoclay. Transmission electron microscopy studies also showed an exfoliated morphology of the nanocomposites. Morphology and thermal properties of the nanocomposites were further examined by means of scanning electron microscopy (SEM) and thermo gravimetric analysis (TGA), respectively. Rheological properties of the EVA40/organoclay nanocomposites were investigated using a rotational rheometer with parallel‐plate geometry in both steady shear and dynamic modes, demonstrating remarkable differences with the clay contents in comparison to that of pure EVA40 copolymer.