Dependence Of Rheological Properties Research Articles

An experimental investigation on the matrix dependent rheological properties of MRE

The rheological properties of magnetorheological elastomers are influenced by magnetically sensitive fillers and the elastomer matrix. The ability to respond to an external magnetic field is imparted by the fillers, while the load-bearing capability is determined by the matrix type. In this paper, the effect of matrix material on the properties of magnetorhological elastomer is explored experimentally. Carbonyl iron particle content is varied by 0%, 15% and 25% by volume to produce magnetorheological elastomer samples using natural rubber, silicone rubber and nitrile butadiene rubber matrices. Forced transmissibility test approach was employed to evaluate the field induced variations in the dynamic stiffness and loss factor of magnetorheological elastomers. The dynamic stiffness of nitrile butadiene rubber is the highest, while that of silicone rubber is the lowest. Addition of carbonyl iron particles significantly improves stiffness, although these gains depend on the properties of unfilled matrix. The addition of 25% by volume of carbonyl iron particle increased the dynamic stiffness of a silicone rubber matrix based magnetorheological elastomer by 67.78%, while the similar change in magnetorheological elastomer with nitrile butadiene rubber matrix was 38.58%. The field dependent response of magnetorheological elastomers is governed by the matrix and ferromagnetic filler concentration. These qualities are higher in magnetorheological elastomer with a low initial dynamic stiffness matrix and lower in magnetorheological elastomers with a stiffer matrix.

Investigation on ethylene glycol and glycerol mixture concentration dependent optical, dielectric, electrical, rheological, and thermophysical properties of EG+Gly/ZnO semiconductor nanofluids

Wide energy bandgap metal oxide nanomaterials containing semiconductor nanofluids (SNFs) are technologically established as advanced multifunctional materials for progress in high performance soft condensed devices. Therefore, to strengthen this field of materials, the present study reports in detail the optical, dielectric, electrical, rheological, and thermophysical properties of the SNFs based on ethylene glycol (EG) and glycerol (Gly) mixture of an entire concentration range (Gly volume fractions; 0.00, 0.25, 0.50, 0.75, and 1.00) with a fixed amount of zinc oxide (ZnO) semiconductor nanomaterial (0.05 wt%). These green-formulated EG + Gly/ZnO SNF materials showed a longer stability of the suspended nanoparticles in the highly viscous hydrogen bonded base fluid and exhibited an increase in absorbance with the decrease wavelength of visible range photons and the ZnO electronic transition at about 3.2 eV energy of ultraviolet radiations. Dielectric measurements over the 20 Hz–1 MHz range of these SNFs, at 298.15 K, explained a dominant contribution of the electrode and interfacial polarization processes at low frequencies and the molecular dipole polarization of static permittivity about 40 at the higher frequencies. Electrode polarization and conductivity relaxation times enhanced exponentially when the Gly concentration increased in the EG + Gly base fluid which governs the electrical conductivity decrement from 0.79 to 0.04 μS/cm for these SNFs. The rheological study explained the Newtonian characteristics of EG + Gly/ZnO nanofluids with their base fluid mixture concentration controllable dynamic viscosity in the wide range of 17–702 mPa s, at 298.15 K. The density, refractive index, ultrasound velocity, prominent acoustic parameters, and thermal conductivity are determined and discussed to explore the solid-liquid interaction and interfaces formed in these innovative SNF materials.

Scaling purely elastic instability of strongly shear thinning polymer solutions.

Flow of viscoelastic polymer solutions in curved channels exhibits instability caused by the elastic nature of polymers even at low Reynolds numbers. However, scaling of the onset of this purely elastic instability in semidilute polymer solutions has not been previously reported. Here we experimentally investigate the flow of highly elastic polymer solutions above their overlap concentrations using pressure measurements and particle image velocimetry. We demonstrate that the onset of instability can be scaled by including shear dependent rheological properties of the polymer solutions in the nonlinear stability analysis. As a result, a universal criterion as function of normalized polymer concentration is provided for scaling the onset of purely elastic instability in the semidilute regime regardless of the type and molecular weight of the polymer.

High shear rate propulsion of acoustic microrobots in complex biological fluids.

Untethered microrobots offer a great promise for localized targeted therapy in hard-to-access spaces in our body. Despite recent advancements, most microrobot propulsion capabilities have been limited to homogenous Newtonian fluids. However, the biological fluids present in our body are heterogeneous and have shear rate–dependent rheological properties, which limit the propulsion of microrobots using conventional designs and actuation methods. We propose an acoustically powered microrobotic system, consisting of a three-dimensionally printed 30-micrometer-diameter hollow body with an oscillatory microbubble, to generate high shear rate fluidic flow for propulsion in complex biofluids. The acoustically induced microstreaming flow leads to distinct surface-slipping and puller-type propulsion modes in Newtonian and non-Newtonian fluids, respectively. We demonstrate efficient propulsion of the microrobots in diverse biological fluids, including in vitro navigation through mucus layers on biologically relevant three-dimensional surfaces. The microrobot design and high shear rate propulsion mechanism discussed herein could open new possibilities to deploy microrobots in complex biofluids toward minimally invasive targeted therapy.

The Effect of Biopolymer Chitosan on the Rheology and Stability of Na-Bentonite Drilling Mud.

The utilization of greens resources is a grand challenge for this century. A lot of efforts are paid to substitute toxic ingredients of the conventional drilling mud system with nontoxic natural materials. In this paper, the effect of the natural polymer chitosan on the rheology and stability of sodium-bentonite drilling mud was investigated in the polymer concentration range of 0.1–3.0 wt.%. Both the shear and time dependent rheological properties of pure chitosan, pure bentonite and bentonite–chitosan dispersions were studied. Moreover, zeta potential measurements were used to evaluate the stability of bentonite-chitosan suspension. Adding chitosan improved the natural properties of drilling mud, namely: yield stress, shear thinning, and thixotropy. The viscosity of bentonite suspension increased significantly upon the addition of chitosan in the concentration range of 0.5 to 3.0 wt.% forming network structure, which can be attributed to the interactions of hydrogen bonding between -OH clusters on the bentonite surface with the NH group in the chitosan structure. On the other hand, dispersed chitosan–bentonite suspension was observed at low chitosan concentration (less than 0.5 wt.%). Increasing both bentonite and chitosan concentrations led to the flocculation of the bentonite suspension, forming a continuous gel structure that was characterized by noteworthy yield stress. The desired drilling mud rheological behavior can be obtained with less bentonite by adding chitosan polymer and the undesirable effects of high solid clay concentration can be avoided.

Thixotropy of magnetorheological gel composites: Experimental testing and modelling

Magnetorheological gel (MRG) is known as an aspiring controllable composite which exhibit rapid and reversible structural changes subjected to magnetic fields. Its rheological manifestation of the structural changes induced by both the shearing flow and the magnetic field is the varying in viscosity or shear stress. This effect is called thixotropy if the structural changes are reversible and time dependent. In this study, time dependent rheological properties were characterised by a proposed stepwise experiment which revealed the effects of shear rate, magnetic field, and resting time on the structural break-down and rebuilding in MRG. The results indicated up to 15% decrease in the shear stress of MRG under the constant shear rate of 6000 1/s within 5 s. 4 s and 30 s of resting allows approx. 50% and 98% recoveries of the reversible structural change, respectively. The application and intensifying of magnetic fields tend to increase thixotropic yield stress but decrease the fluctuation state. A simple model was formulated to capture the unique time dependent structural changes of MRG under constant shear flow and magnetic field; and, showed accurate predictions of the thixotropic responses of MRG under the magnetic fields, shear rates and resting time considered.

Effect of temperature on the SU‐8 photoresist filling behavior during thermal nanoimprinting

AbstractSU‐8 photoresist is an ideal thermal‐imprinting polymer, which has been widely used in micro‐nano devices in recent years. However, the research on the filling behavior of SU‐8 photoresist during thermal nanoimprinting is not complete. In this paper, the stress relaxation curves and shear stress/rate flow curves were measured to analyze the temperature dependent rheological properties of SU‐8 photoresist. The filling behavior of SU‐8 photoresist was discussed based on thermal imprinting results at various temperatures. High‐precision nanochannels were fabricated with replication error of 2.8% at optimized thermal imprinting temperature of 85°C and duration of 10 min, which paves the way for high‐precision fabrication of SU‐8‐based micro‐nanofluidic chips.

COMPARISON OF FRESH AND HARDENED PROPERTIES OF SELF-COMPACTING CONCRETE MIXTURE FROM DIFFERENT ASPECT RATIO OF STEEL FIBER VIEW POINT

ABSTRACT Self-compacting concrete (SCC) is a type of concrete which is frequently preferred in different applications due to its advantages such as its fluidity and transition in tight openings between steel reinforcing bars. However, it is vital that SCC maintains its fresh state characteristics when its transportation phase is taken into consideration. Fiber reinforced in SCC affects the properties of fresh concrete negatively while it had a positive effect on its dynamic properties. In this study, the effect of steel fibers having different aspect ratios on the time dependent fresh properties and mechanical properties of self-compacting concrete mixtures was investigated. In addition to the control mixture without fiber, in the mixtures containing fiber, three different twin-hook steel fibers with aspect ratios of 54, 64 and 50 were used as 0.6% of total volume. In all of the SCC mixtures, the water/cement ratio, cement dosage and slump-flow value were kept constant. The time dependent rheological properties of the mixtures were investigated. The compressive, split-tensile and flexural strengths as well as fracture energy, the load deflection relation under flexural load and load-crack opening displacement, modulus of elasticity of SCC mixtures were also investigated. Besides, the water absorption capacity and depth of penetration of water under pressure of mixtures were measured. On the basis of the results, the fiber utilization and its aspect ratio had no significant effect on compressive strength and modulus of elasticity of the SCC mixtures. The split-tensile, flexural strengths and fracture energy of SCC mixtures increased by using fiber; the permeability properties of SCC mixture increased by fiber utilization.

Preparation of Electron/Ion-Mixed Conducting Gel Using Liquid Metal and Ionic Liquid

Introduction Eutectic gallium-indium (Ga-In) has excellent properties, such as low melting point of 15.3 °C, high thermal and electronic conductivity, and metallic luster. Ga-In has promise as a liquid electron-conducting material owing to its low viscosity, negligible vapor pressure and low toxicity.1, 2) On the other hand, ionic liquids are ambient temperature molten salts that have attracted considerable attention because of unique properties such as high ionic conductivity, non-volatility and thermal stability. We proposed that ion gels, composed of macromolecular networks swollen with ionic liquids, exhibit self-standing film-forming ability in addition to the unique properties of ionic liquids. In this study, we prepared composite gel materials containing ionic liquid and Ga-In. This composite gel (metal gel) might have high electronic conductivity based on Ga-In and high ionic conductivity originated from the ionic liquid, as well as good mechanical properties based on the polymer, such as flexibility and strechability. These new materials are applicable to flexible or stretchable devices in wearable and flexible electronics applications. Experimental We chose hydrogen bonding copolymers of N,N-dimethylacrylamide (DMAAm) and acrylic acid (AAc) (P(DMAAm-r-AAc)) as the matrix polymers. This copolymer was combined with a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([C2mim][NTf2]) to form an ion gel.3) In order to improve dispersibility of Ga-In in the composite gel, bulk Ga-In was ultra-sonicated in ethanol and the suspension of Ga-In microdroplets was mixed with P(DMAAm-r-AAc) and [C2mim][NTf2]. The composite gels were prepared by solution casting method either in the air where thin oxide layer is formed on the Ga-In particles4) or under inert atmosphere to examine the effects of preparation conditions on their properties. Results and Discussion In tensile tests, Young’s modulus increased with increasing volume fraction of Ga-In in the composite gels. In rheological measurements, storage modulus was higher than loss modulus, confirming soft solid-like behavior of the composite gels. In both measurements, modulus of composite gels was higher than that of ion gels. We found difference in the temperature dependent rheological properties between the composite gels prepared in air and under inert atmosphere. The presence/absence of the surface oxide layer on the Ga-In particles was likely responsible for the difference in the rheological responses. Electronic conductivity was improved by a factor of 106 for the composite gels prepared under inert atmosphere compared to that of the composite gels prepared in the air. It was found that the oxide layers on the Ga-In particles had a significant impact on the rheological and electronic properties. However, electronic conductivity of the composite gels prepared under inert atmosphere was still low compared to that of bulk Ga-In. To achieve high electronic conductivity comparable to the bulk value, volume fraction of Ga-In microdroplets needs to be increased in the composite gels. In order to improve dispersibility of high-loading Ga-In in the composite gel, Ga-In microdroplets were prepared with dispersants. The results suggested that there is a trade-off between dispersibility of the Ga-In microdroplets and the electronic conductivity: better dispersibility of Ga-In microdroplets resulted in lower electronic conductivity. Acknowledgement This study was supported in part by Core Research for Evolutionary Science and Technology (CREST) of the Japan Science and Technology Agency (JST). References 1) Kazem, N. et al, Adv. Mater., 2017, 29, 1-14.2) Anderson, T. J. et al, Phase Equilibria, 1991, 12, 64-72.3) Tamate, R. et al, Adv. Mater, 2018, 30, 18027924) Ren, L. et al, Adv. Funct. Mater., 2016, 26, 8111-8118. Figure 1

A novel approach to characterize the magnetic field and frequency dependent dynamic properties of magnetorheological elastomer for torsional loading conditions

Magnetorheological elastomers (MRE) are potential resilient elements to improve the operating frequency range of a vibration isolator. The field-dependent characterization of MRE properties for varying input frequencies under lateral shear conditions has been well researched in past studies. In the present study, a novel approach to assess the magnetic field dependent rheological properties of magnetorheological elastomers under dynamic torsional loading is presented. Field and frequency-dependent properties are estimated from the dynamic blocked transfer stiffness method specified by ISO 10846. Viscoelastic properties represented in-terms of complex torsional stiffness and loss factor are estimated from the Lissajous curves within the linear viscoelastic (LVE) limit. Experiments are performed at a frequency range of 10 Hz–30 Hz under a constant input angular displacement. Magnetic field sensitive characteristics of MRE are evaluated under the field produced by a custom-made electromagnet. The results reveal a strong influence of field dependent variations on the complex stiffness in comparison with the input frequency. Variations observed in the loss factor suggests a dominance of the imaginary part of the complex stiffness on the energy dissipation. The reduced field induced enhancements in the complex stiffness are interpreted from the Magneto-static and structural based numerical simulations using ANSYS 19.1.

Fluid medium effect on stresses in suspensions of high-inertia rod-like particles

The rheology of suspensions of high-inertia (or granular) non-spherical particles characterized by high particle Stokes and Reynolds numbers is rarely investigated. In this study, we investigate the rheology of suspensions of inertial rod-like particles of aspect ratio 4 subjected to shear flow. In particular, the effect of fluid medium (air, water) against dry granular simulations on the developed stresses is assessed. CFD-DEM simulations are performed for a periodic shear box for a range of shear rates and volume fractions of particles. The dependence of rheological properties like shear stress, normal stress difference, pressure and relative viscosity on volume fraction, shear rate, granular temperature and the particle orientation are discussed. These results provide insight into the macroscopic rheology of suspensions of rods and demonstrate that the effect of particle shape and surrounding fluid cannot be completely ignored. Air as a fluid medium shows similar scaling as compared to dry granular simulations, but the stress values are generally lower. We observe drastic change in both scaling and values for water as fluid medium. In all cases, the rods show strong alignment in the direction of shear. This study can be further extended to develop stress closures for use in Eulerian flow models.

Magnetorheological suspension with capillary network

The capillary force has been employed to facilitate an effective pathway for the preparation and design of magnetorheological suspensions. The network formation from pendular particle structure-driven assembly can potentially be used to stabilize particle suspension. Furthermore, the magnetic liquid bridge proposed can give rise to a dramatic enhancement in magnetorheological effect (20%–100% increment in storage modulus), suggesting the possibility of tuning field dependent rheological properties of magnetorheological suspensions by addition of minute amounts of ferrofluid.

On the Possibility of Using Epoxy Prepregs for Carcass-Inflatable Nanosatellite Antennas

The possibility of using epoxy prepregs (fabric impregnated with epoxy resin) for carcass-inflatable antennas on space nanosatellites was investigated. It is shown that the optimal method of obtaining such devices is the use of reactive mixtures of hot cure, when the chemical reaction of curing of antenna deployed in space occurs under the action of solar radiation. In this case, the antenna is put into orbit in the nanosatellite in a compact form and no additional mechanisms are needed to give it the final working shape. The rheological properties of the mixture of epoxy resin YD-128 with hardener TEAT-1, suitable for making hot-curing prepregs and its use in near-earth orbit, are investigated. The dependence of rheological properties on temperature, hardener concentration and curing time is established. With the help of computer simulation, the temperature is calculated, to which the antenna carcass can be heated in near-earth orbit under the influence of thermal radiation from the Sun and the Earth taking into account its orientation in relation to the sources of heat. It is established that the process of hot curing of the antenna is possible due to solar and terrestrial radiation only when the frame is covered with a thin metallized layer that is close in characteristics to the layer of aluminum foil.

Optimal design of structure in rheological models: an automotive application to dampers with high viscosity silicone fluids

Dynamic torsional vibration dampers are for a long time inherent integral components of internal combustion engines. One of the most common types of the dynamic dampers is a silicone damper. It has been, for many years, perceived as an exclusively viscous damper, thus it has been constructed and designed according to this perception. When compared to other types of dynamic dampers of the similar size with flexible components used for their construction, the standard viscous damper has a lower damping effect. Moreover, this damper type has been a significantly cheaper and simpler solution. Current silicone oils with high nominal viscosity, having not only the expected damping properties, but also significant elastic characteristics under alternate shear stress, enable construction of dynamic dampers with a higher damping effect than a viscous damper. Frequency and temperature dependent complicated rheological properties of high viscosity silicone fluids can only be identified experimentally using a suitable dynamic viscometer. However, the measured frequency dependencies of both components of the complex shear modulus are only defined for harmonic loading while internal combustion engine load is periodic and contains several tens harmonics. The key to the solution is therefore to find suitable multiparameter rheological models comprised of linear elastic and damping elements that would approximate in the specified frequency range both components of the complex shear modulus. Such a complicated task can be solved using efficient optimization algorithms. This article focuses on the mathematical description of convolute rheological properties of high viscosity silicone liquids and also contains an example of the application of created rheological models in the complex dynamic model of a V10 diesel engine. A computational tool for the determination of stiffness and damping coefficients of the multi-parameter rheological model was created and solved in the optimization software GAMS by means of the CONOPT solver. The possibility of these modern technologies is shown by the comparison of computation models and experimentally set torsional vibration spectres with standard viscous damper and damper utilizing a high viscosity silicone oil.

Formation of a physical crosslinked structure in polydimethylsiloxanes modified with long-chain hydrocarbon substituents with polar fragments

The dependence of rheological properties (viscosity and dynamic moduli G′ and G″) and time for formation of a physical network for polydimethylsiloxanes bearing ester and amide groups in aliphatic substituents at silicon atoms on the concentration of modifying units, the heating temperature, and the time of curing at elevated temperatures is studied.

Design of a C-b-(A-co-B)-b-C telechelic polyampholyte pH-responsive gelator

We report the synthesis and the pH dependent structural and rheological properties of a telechelic polyampholyte associative polymer, composed of a random polyampholyte central block, end-capped by shorter hydrophobic blocks [C-b-(A-co-B)-b-C block/random terpolymer type].

Assessment of resin adhesives aging by means of rheological parameters, Inverse Gas Chromatography, and FTIR

In this study, the rheological parameters as well as Flory–Huggins parameter determined by Inverse Gas Chromatography (IGC) were applied for assessment of the changes occurring during storage of the resole resin and their composites. It was proved that storage of resole and its composites at the low temperature (about 10°C) can slow significantly the process of their aging. Main idea of research was to determine time dependence of rheological properties for resole resin. These data should enable to extend shelf life of resin containing products. The rheological properties of samples were studied by the determination of flow curve. Share rate was changed from 10 to 500 1/s. Samples were examined in following intervals (increasing storage time): immediately after preparing the sample and then after storage, respectively: after two, four, eight, and twelve weeks. To extend shelf life of resin, it was mixed with different additives: zeolite Micro 20, Mg(OH)2, PAF, synthetic zeolites: sodium form Z1, hydrogen form Z2. Flory–Huggins parameter determined by use of IGC let to assess physicochemical changes occurring in resole and its composites during storage. IGC turned out to be more sensitive method for assessment of changes occurring during resin aging than rheological measurements. FTIR technique was used to assess chemical changes occurring during resoles compositions storage. It indicated that oxidation reaction can occur during resoles composite aging.

Functional properties of Balangu seed gum over multiple freeze–thaw cycles

In this study, the effect of three freeze/thaw cycles (FTCs), two freezing temperatures and different gum concentrations on some functional properties of Balangu seed gum (BSG), including the time-independent and -dependent rheological properties, textural characteristics, and emulsifying and foaming capabilities were investigated. BSG exhibited strong shear thinning and thixotropy that were influenced by the FTCs. Freeze/thaw treatments increased the yield stress, consistency coefficient, initial and equilibrium shear stresses, while the flow behavior index remained almost constant, although the impact of lower temperature and higher concentration was more pronounced. BSG demonstrated an excellent water holding capacity, so that no syneresis was observed during the FTCs. Textural, emulsifying and foaming properties of BSGs were enhanced by concentration increment and FTCs. The results indicated excellent functional properties of BSG, which can be used in frozen foods to decrease the destructive effects of ice crystals growth.

Influence of Temperature on Energetic and Rheological Characteristics of PLANTOHYD Bio Lubricants – a Study in the Laboratory

This article presents the results of measuring the calorific value and the rheological characteristics of Plantohyd bio lubricants. Measurements were conducted under laboratory conditions with an IKA C5000 calorimeter and a DV-3P Anton Paar digital viscometer. Results are presented graphically. It is shown that the physical interpretation of energy values results ​​and the dependence of rheological properties on temperature can be used to assess the quality of lubricants.

Rate dependent biomechanical properties of corneal stroma in unconfined compression

The corneal stroma is a highly ordered extracellular matrix and mainly responsible for the mechanical strength of the cornea. The rate dependent mechanical and rheological properties of the cornea are not completely understood and there is large variation in the reported estimates. In this work, the rate dependent mechanical behavior of the corneal stroma was investigated using experimental studies and theoretical models. Unconfined compression stress-relaxation experiments at different displacement rates and compressive strains were conducted. The unconfined compression material parameters, i.e. corneal out-of-plane modulus, in-plane modulus and permeability coefficient were determined from curve-fitting the experimental data with a transversely isotropic biphasic model. It was found that the maximum force reached during the step loading increased with both increasing magnitude and rate of the compressive strain. It was also observed that at all loading rates the in-plane Young's modulus increased with increasing strain, while the permeability coefficient decayed with increasing compressive strain. At a constant compressive strain, both the in-plane Young's modulus and the permeability coefficient increased with increasing the loading rate. Regardless of loading rates and compressive strains, a range of corneal out-of-plane modulus of 0.6 kPa to 13.8 kPa, in-plane modulus of 0.5 MPa to 4.8 MPa, and permeability coefficient of 1×10⁻¹⁴ m⁴/N·s to 7×10⁻¹⁴ m⁴/N·s was found.