Showing papers on "Rheometer published in 2014"
TL;DR: The potential for LIS to reduce drag in laminar flows is demonstrated and the dependence of drag reduction on the ratio of the viscosity of the working fluid to that of the lubricant is elucidated.
Abstract: Lubricant-impregnated surfaces (LIS), where micro/nanotextured surfaces are impregnated with lubricating liquids, have received significant attention for their robust, superslippery properties. In this study, we systematically demonstrate the potential for LIS to reduce drag in laminar flows. We present a scaling model that incorporates the viscosity of the lubricant and elucidates the dependence of drag reduction on the ratio of the viscosity of the working fluid to that of the lubricant. We experimentally validate this dependence in a cone and plate rheometer and demonstrate a drag reduction of 16% and slip length of 18 μm in the case where the ratio of working fluid viscosity to lubricant viscosity is 260.
244 citations
TL;DR: In this article, the rheological behavior of sodium alginate (SA) aqueous solutions was analyzed using an Anton Paar-Physica MCR 301 Rheometer and it was found that, above a critical shear rate, all G-rich SA solutions exhibited non-Newtonian shear-thinning behavior and the flow curves could be well described by the Cross model.
154 citations
TL;DR: The present work systematically analyzed protein adsorption kinetics in terms of surface pressure rise using a drop profile analysis tensiometer and addressed the interfacial layer properties under shear stress using an interfacial shear rheometer under the same experimental conditions.
115 citations
TL;DR: In this article, the rheological behavior of concentrated aqueous dispersions of graphene oxide (GO) was studied as a model system and then compared to those of GO in poly(methyl methacrylate) (PMMA).
Abstract: The rheological behaviour of concentrated aqueous dispersions of graphene oxide (GO) was studied as a model system and then compared to those of GO in poly(methyl methacrylate) (PMMA). Dynamic and steady shear tests were conducted using a parallel plate rheometer. The aqueous system behaved as a reversibly flocculated dispersion with linear viscoelastic regions (LVR) extending up to strains of 10 %. Dynamic frequency sweeps conducted within the LVR showed a classic strong-gel spectrum for high concentrations. Under steady shear, the dispersions shear-thinned up to a Peclet number (Pe) <1, followed by a power law at higher Pe. The dispersions were thixotropic and recovered their structure after 60 min rest. The change in rheological properties of the PMMA upon the addition of the GO was less pronounced possibly due to the absence of hydrogen bonding; a relatively small increase in viscosity was found, which is encouraging for the melt processing of graphene composites.
93 citations
TL;DR: The Sliding Pipe Rheometer (Sliper) is a new device developed to resolve this problem and provide reliable estimations of pumping pressures as discussed by the authors. But it is not suitable for the use of concrete.
92 citations
TL;DR: In this article, the effect of viscosity modifier nature and concentration on the rheological properties of model oil-based drilling fluids (OBM) submitted to high pressure was investigated.
92 citations
TL;DR: In this article, the effect of wood cell wall composition on the rheological properties of wood particle/high density polyethylene (HDPE) blends was investigated, and the results showed that removal of lignin and/or hemicelluloses changed the crystallinity and microstructure of cell walls.
85 citations
TL;DR: Evidence of a bulk yield stress arising from protein aggregation is presented, and correlated with results from standard characterization techniques used in the bio-pharmaceutical industry.
Abstract: A combination of sensitive rotational rheometry and surface rheometry with a double-wall ring were used to identify the origins of the viscosity increase at low shear rates in protein solutions. The rheology of two high molecular weight proteins is discussed: Bovine Serum Albumin (BSA) in a Phosphate Buffered Saline solution and an IgG1 monoclonal antibody (mAb) in a formulation buffer containing small quantities of a non-ionic surfactant. For surfactant-free BSA solutions, the interfacial viscosity dominates the low shear viscosity measured in rotational rheometers, while the surfactant-laden mAb solution has an interfacial viscosity that is small compared to that from aggregation in the bulk. A viscoelastic film forms at the air/water interface in the absence of surfactant, contributing to an apparent yield stress (thus a low shear viscosity increase) in conventional bulk rheology measurements. Addition of surfactant eliminates the interfacial yield stress. Evidence of a bulk yield stress arising from protein aggregation is presented, and correlated with results from standard characterization techniques used in the bio-pharmaceutical industry. The protein film at the air/water interface and bulk aggregates both lead to an apparent viscosity increase and their contributions are quantified using a dimensionless ratio of the interfacial and total yield stress. While steady shear viscosities at shear rates below ∼1 s(-1) contain rich information about the stability of protein solutions, embodied in the measured yield stress, such low shear rate data are regrettably often not measured and reported in the literature.
78 citations
TL;DR: In this paper, an alternative method based on the use of silicon microcantilevers is presented, which is based on analytical equations for the hydrodynamic force, permits the measurement of the complex shear modulus of viscoelastic fluids over a wide frequency range.
Abstract: At the microscale, cantilever vibrations depend not only on the microstructure’s properties and geometry but also on the properties of the surrounding medium. In fact, when a microcantilever vibrates in a fluid, the fluid offers resistance to the motion of the beam. The study of the influence of the hydrodynamic force on the microcantilever’s vibrational spectrum can be used to either (1) optimize the use of microcantilevers for chemical detection in liquid media or (2) extract the mechanical properties of the fluid. The classical method for application (1) in gas is to operate the microcantilever in the dynamic transverse bending mode for chemical detection. However, the performance of microcantilevers excited in this standard out-of-plane dynamic mode drastically decreases in viscous liquid media. When immersed in liquids, in order to limit the decrease of both the resonant frequency and the quality factor, and improve sensitivity in sensing applications, alternative vibration modes that primarily shear the fluid (rather than involving motion normal to the fluid/beam interface) have been studied and tested: these include in-plane vibration modes (lateral bending mode and elongation mode). For application (2), the classical method to measure the rheological properties of fluids is to use a rheometer. However, such systems require sampling (no in-situ measurements) and a relatively large sample volume (a few milliliters). Moreover, the frequency range is limited to low frequencies (less than 200Hz). To overcome the limitations of this classical method, an alternative method based on the use of silicon microcantilevers is presented. The method, which is based on the use of analytical equations for the hydrodynamic force, permits the measurement of the complex shear modulus of viscoelastic fluids over a wide frequency range.
70 citations
TL;DR: In this paper, the authors propose a novel device capable of measuring relaxation times of viscoelastic fluids as small as 1 ms. In contrast to most rheometers, which by their very nature are concerned with producing viscometric or nearly-viscometric flows, here they make use of an elastic instability that occurs in the flow of vis coelastic fluid with curved streamlines.
Abstract: We propose a novel device capable of measuring relaxation times of viscoelastic fluids as small as 1 ms. In contrast to most rheometers, which by their very nature are concerned with producing viscometric or nearly-viscometric flows, here we make use of an elastic instability that occurs in the flow of viscoelastic fluids with curved streamlines. To calibrate the rheometer we combine simple scaling arguments with relaxation times obtained from first normal-stress difference data measured in a classical shear rheometer. As an additional check we also compare these relaxation times to those obtained from Zimm theory and good agreement is observed. Once calibrated, we show how the serpentine rheometer can be used to access smaller polymer concentrations and lower solvent viscosities where classical measurements become difficult or impossible to use due to inertial and/or resolution limitations. In the absence of calibration, the serpentine channel can still be a very useful comparative or index device.
67 citations
TL;DR: Interestingly, it is found that aggregated interfaces transition to yielding well before they reached a jammed state, indicating that the mechanics of these interfaces are not simply jammed or unjammed and that the interfacial rheology relationship with microstructure can give significant insight into understanding how to engineer particle laden interfaces in the future.
Abstract: The study of particle laden interfaces has increased significantly due to the increasing industrial use of particle stabilized foams and Pickering emulsions, whose bulk rheology and stability are highly dependent on particle laden interface’s interfacial rheology, which is a function of interfacial microstructure. To understand the physical mechanisms that dictate interfacial rheology of particle laden interfaces requires correlating rheology to microstructure. To achieve this goal, a double wall ring interfacial rheometer has been modified to allow real time, simultaneous interfacial visualization and shear rheology measurements. The development of this tool is outlined, and its ability to provide novel and unique measurements is demonstrated on a sample system. This tool has been used to examine the role of microstructure on the steady shear rheology of densely packed, aggregated particle laden interfaces at three surface concentrations. Through examination of the rheology and analysis of interfacial mi...
TL;DR: In this article, the behavior of microfibrillated cellulose (MFC) water suspensions was characterized with a rotational rheometer, augmented with optical coherence tomography (OCT).
Abstract: Rheology of microfibrillated cellulose (MFC) water suspensions was characterized with a rotational rheometer, augmented with optical coherence tomography (OCT) To the best of the authors’ knowledge, this is the first time the behavior of MFC in the rheometer gap was characterized by this real-time imaging method Two concentrations, 05 and 1 wt% were used, the latter also with 10−3 and 10−2 M NaCl The aim was to follow the structure of the suspensions in a rotational rheometer during the measurements and observe wall depletion and other factors that can interfere with the rheological results The stepped flow measurements were performed using a transparent cylindrical measuring system and combining the optical information to rheological parameters OCT allows imaging in radial direction from the outer geometry boundary to the inner geometry boundary making both the shear rate profile and the structure of the suspension visible through the rheometer gap Yield stress and maximum wall stress were determined by start-up of steady shear and logarithmic stress ramp methods and they both reflected in the stepped flow measurements Above yield stress, floc size was inversely proportional to shear rate Below the yield stress, flocs adhered to each other and the observed apparent constant shear stress was controlled by flow in the depleted boundary layer With higher ionic strength (10−2 M NaCl), the combination of yield stress and wall depletion favored the formation of vertical, cylindrical, rotating floc structures (rollers) coupled with a thicker water layer originating at the suspension—inner cylinder boundary at low shear rates
TL;DR: This work has identified multiple aspects of particle-tracking microrheology that can contribute to orders-of-magnitude disagreement with macrorheological methods and shows that compressibility or Marangoni stress related effects may be contributing to the orders of magnitude disagreement in micro and macror heological measurements observed in the hexadecanol system.
Abstract: Interfacial transport phenomena play an important role in the dynamics of liquid interfaces found in emulsions, foams, and membranes. Both macroscopic and microscopic measurements of interfacial transport and rheology can be made, the former typically relying on the use of at least millimeter-scale probes, and the latter exploiting the motion of micrometer-scale probes. Recent publications have shown multiple orders of magnitude differences between experimentally observed diffusivities in passive microrheology, and the diffusivities expected based on macroscopic measurements of the surface rheology. In the present work, interfacial rheological measurements were made with both microrheological and macrorheological methods and the results are compared for different monolayers at an air–water interface. We have identified multiple aspects of particle-tracking microrheology that can contribute to orders-of-magnitude disagreement with macrorheological methods. In particular, unintentional tracking of particles not residing at the interface, the presence of large-scale interfacial heterogeneities, and underestimating static noise can all decrease estimates of surface viscosity from particle-tracking microrheology by orders of magnitude. After taking care to address these artifacts, we show that viscosities obtained from both methods agree well for poly(tert-butyl methacrylate) (PtBMA), and for dipalmitoylphosphatidylcholine (DPPC), but disagree by orders of magnitude for hexadecanol. In poly(tert-butyl acrylate) (PtBA), large-scale heterogeneities prevented us from obtaining representative surface viscosities. By making surface viscosity measurements in an interfacial stress rheometer (ISR) with needles of different aspect ratio, we show that compressibility or Marangoni stress related effects may be contributing to the orders of magnitude disagreement in micro and macrorheological measurements observed in the hexadecanol system.
TL;DR: In this article, the effects of temperature, pressure, dissolved carbon dioxide and shear rate on the rheological response of bitumen are investigated by using the reduced variable method at the temperature range of −10°C to 180°C and pressures up to 15MPa.
TL;DR: This work examines the simplest relevant molecular model for large-amplitude shear (LAOS) flow of a polymeric liquid: the suspension of rigid dumbbells in a Newtonian solvent, and finds the shapes of the shear stress versus shear rate loops predicted to be reasonable.
Abstract: We examine the simplest relevant molecular model for large-amplitude shear (LAOS) flow of a polymeric liquid: the suspension of rigid dumbbells in a Newtonian solvent. We find explicit analytical expressions for the shear rate amplitude and frequency dependences of the first and third harmonics of the alternating shear stress response. We include a detailed comparison of these predictions with the corresponding results for the simplest relevant continuum model: the corotational Maxwell model. We find that the responses of both models are qualitatively similar. The rigid dumbbell model relies entirely on the dumbbell orientation to explain the viscoelastic response of the polymeric liquid, including the higher harmonics in large-amplitude oscillatory shear flow. Our analysis employs the general method of Bird and Armstrong ["Time-dependent flows of dilute solutions of rodlike macromolecules," J. Chem. Phys. 56, 3680 (1972)] for analyzing the behavior of the rigid dumbbell model in any unsteady shear flow. We derive the first three terms of the deviation of the orientational distribution function from the equilibrium state. Then, after getting the "paren functions," we use these for evaluating the shear stress for LAOS flow. We find the shapes of the shear stress versus shear rate loops predicted to be reasonable.
TL;DR: In this article, the role of particle concentration, polymer concentration, and polymer molecular weight on both the shear and the elongational behavior of the dispersions was examined and it was found that increasing particle concentration was found to increase the degree of shear thickening.
Abstract: In this paper, the shear and extensional rheology of fumed silica nanoparticles dispersed in an aqueous polyethylene oxide (PEO) solution is investigated. The role of particle concentration, polymer concentration, and polymer molecular weight on both the shear and the elongational behavior of the dispersions was examined. The fumed silica dispersions were found to strongly shear thicken. Increasing particle concentration was found to increase the degree of shear thickening. The effect of polymer concentration and polymer molecular weight on shear-thickening behavior was found to be nonmonotonic. The data showed a maximum in shear thickening at an optimum polymer concentration and molecular weight. Increasing the polymer concentration and molecular weight was found to reduce the critical shear rate for the onset of shear thickening. Linear viscoelastic measurements showed a qualitatively similar trend in the elastic modulus. Extensional rheology was conducted using a capillary breakup extensional rheometer. The dispersions showed strong strain-hardening behavior with thickening magnitudes similar to that observed under shear. The trends in the magnitude of extensional hardening with particle and polymer concentration were found to be similar to shear. In some cases, extensional thickening of nearly 1000 times was observed. However, in contrast to shear, increasing the molecular weight of the PEO corresponded to a sharp increase in extensional strain-hardening likely due to the role of polymer-induced elasticity which was shown to cause extensional hardening even in the absence of nanoparticles.
TL;DR: In this article, the rate of diffusion of a virgin binder into a reclaimed asphalt pavement (RAP) binder, which controls the blending of two binders during exposure, was evaluated at varying levels.
Abstract: There are many concerns about the blending between virgin and aged binders in reclaimed asphalt pavement (RAP). Determining the extent of the blending and identifying the main factors affecting the blending between two binders have gained great interest in recent years. Viscosity as a function of temperature, exposure time, and film thickness have been mentioned as the main factors controlling the blending between two binders that are in contact. The in-contact blending between two binders is hypothesized to be governed by a diffusion phenomenon in which material is transferred through a medium because of the Brownian motion of molecules. This study aimed to estimate the rate of diffusion of virgin binder (as the diffusing matter) into the RAP binder, which controls the blending of two binders during exposure. The effect of temperature, which was considered as the main factor influencing the diffusion rate, was evaluated at varying levels. Fick's law calculations and dynamic shear rheometer (DSR) measurem...
TL;DR: In this article, a stress-controlled rheometer was used to explore the thixotropic behavior of Mayan crude oil and found that it exhibits non-Newtonian rheological behavior at lower temperatures.
Abstract: Heavy oil and bitumen exhibit non-Newtonian rheological behaviors at lower temperatures. Thixotropy is one such behavior. Thixotropy affects the efficiency and length scale of mixing during blending operations and flow behaviors in pipes and pipelines following flow disruption, where it affects the pressure required to reinitiate flow. In the present work, thixotropic behaviors of Maya crude oil are explored systematically using a stress-controlled rheometer. Maya crude oil is shown to be a shear-thinning fluid below 313 K. The thixotropic behaviors are identified and explored using transient stress techniques (hysteresis loops, stepwise change in the shear rate, and startup experiments). The magnitude of the thixotropy effect is larger at lower temperatures. Relationships are identified between rest times and other thixotropic parameters, such as hysteresis loop area and stress decay, in startup experiments. Stress growth, which occurs as a result of a step-down in the shear rate, is shown to correlate w...
TL;DR: An important prediction is that pronounced banding can arise transiently in each of these protocols, even in fluids for which the underlying constitutive curve of stress as a function of s...
Abstract: We study theoretically the formation of shear bands in time-dependent flows of polymeric and wormlike micellar surfactant fluids, focussing on the protocols of step shear stress, step shear strain (or in practice a rapid strain ramp), and shear startup, which are commonly studied experimentally. For each protocol we perform a linear stability analysis to provide a fluid-universal criterion for the onset of shear banding, following our recent letter [Moorcroft and Fielding, Phys. Rev. Lett. 110, 086001 (2013)]. In each case this criterion depends only on the shape of the experimentally measured rheological response function for that protocol, independent of the constitutive properties of the material in question (Therefore our criteria in fact concern all complex fluids and not just the polymeric ones of interest here.). An important prediction is that pronounced banding can arise transiently in each of these protocols, even in fluids for which the underlying constitutive curve of stress as a function of strain-rate is monotonic and a steadily flowing state is accordingly unbanded. For each protocol we provide numerical results in the rolie-poly and Giesekus models that support our predictions. We comment on the ability of the rolie-poly model to capture the observed experimental phenomenology and on the failure of the Giesekus model.
TL;DR: In this paper, a bucket-vane viscometer was used for the characterization of nanofibrillated cellulose suspensions at the consistency range of 1.3% w/w.
Abstract: This paper discusses the practical application of a bucket vane viscometer in the characterization of novel nanofibrillated cellulose suspensions. Specifically, we use two different grades of nanocellulose, Masuko grinded and TEMPO oxidized ones. We work at the consistency range of 1–2.3 % w/w. We find, in agreement to more accurate rheometer based experiments, that both these materials behave in a highly non-linear manner. Thus, as we discuss in this paper, using a wide gap device necessitates the use of a correction algorithm in the conversion of the angular velocity to global shear rate to access the materials intrinsic, geometry independent, flow behavior. Furthermore, from the application viewpoint, we find that the classically measured low shear rate viscosity is not a good quantity to characterize these materials.
TL;DR: In this article, the chemo-rheology of an industrial polyester system specifically prepared for a pultrusion process is characterized using differential scanning calorimetry (DSC).
Abstract: In the present work, the chemo-rheology of an industrial “orthophthalic” polyester system specifically prepared for a pultrusion process is characterized. The curing behaviour is first characterized using the differential scanning calorimetry (DSC). Isothermal and dynamic scans are performed to develop a cure kinetics model which accurately predicts the cure rate evolutions and describes the curing behaviour of the resin over a wide range of different processing conditions. The viscosity of the resin is subsequently obtained from rheological experiments using a rheometer. Based on this, a resin viscosity model as a function of temperature and degree of cure is developed and predicts the measured viscosity correctly. The evolution of the storage and loss moduli are also measured as a function of time using the rheometer which provides an information about the curing as well as the gelation. The temperature- and cure-dependent elastic modulus of the resin system is determined using a dynamic mechanical analyzer (DMA) in tension mode. A cure hardening and thermal softening model is developed and a least squares non-linear regression analysis is performed. The variation in elastic modulus with temperature and phase transition is captured for a fully cured resin sample
TL;DR: There was a considerable variation in the resin composite viscosities measured at 25°C as an average value for shear-rate sweep, with Filtek Supreme XTE showing the highest viscosity at both temperatures (p<0.05).
TL;DR: In this article, the authors report the first multiplexed microfluidic viscometer capable of measuring simultaneously the viscosity as a function of shear rate for multiple samples.
Abstract: We report the first multiplexed microfluidic viscometer capable of measuring simultaneously the viscosity as a function of shear rate for multiple samples. The viscometer is based on a flow-comparator technique where the interface location between co-flowing streams of test and reference fluids is a sensitive function of the viscosity mismatch between the two fluids. We initially design a single microfluidic viscometer and study two different modes of comparator operation—the interface displacement (ID) mode and the interface compensation mode (IC). We find that both modes yield viscosity curves for Newtonian and polymeric fluids that are consistent with a conventional rheometer. Based on the results from the single microfluidic viscometer, we present an operating window that serves as a guide to assess accessible viscosities and shear rates. We then design a 4-plex and 8-plex viscometer based on the ID mode and show that it is capable of reliably measuring viscosity curves for Newtonian fluids, polymeric solutions and consumer products. Collectively, our results demonstrate that the multiplexed viscometer is capable of measuring in a parallel format, viscosities of fluids spanning nearly three orders of magnitude (≈10−3–1 Pa s) across a shear rate range of ≈1–1,000 s−1. We believe our multiplexed viscometer is a low cost and high-throughput alternative to conventional rheometers that analyze samples serially using expensive robotic liquid-handling systems. The multiplexed viscometer could be useful for rapidly analyzing a wide selection of complex fluids on-site during product formulation and quality control.
TL;DR: In this article, the use of dynamic mechanical analysis (DMA) for assessment of t90 was assessed and the results revealed that the curve of tan δ was able to be used to derive the t90 for rubber compounds.
Abstract: The degree of vulcanization of a rubber compound has a big influence on the properties of the final product. Therefore, precisely defining the curing process including optimum cure time is important to ensure the production of final products having high performance. Typically, vulcanization is represented using vulcanization curves. The main types of equipment used for producing vulcanization curves are the oscillating disc rheometer (ODR) and the moving die rheometer (MDR). These can be used to plot graphs of torque versus time at a constant temperature to show how cure is proceeding. Based on the results obtained, optimum cure time (t90) is calculated as the time required for the torque to reach 90% of the maximum achievable torque. In this study, the use of Dynamic Mechanical Analysis (DMA) for assessment of t90 was assessed. DMA was carried out using shear mode isothermal tests to measure the changes in material properties caused by vulcanization. The results revealed that the shear storage modulus (G′), shear loss modulus (G′′), and tan δ all reflect the vulcanization process, however, tan δ gave the best representation of level of vulcanization. Indeed, the curve of tan δ was able to be used to derive the t90 for rubber compounds and showed good agreement with the results from an MDR. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014, 131, 40008.
TL;DR: In this article, straight and hooked end steel fibers with different lengths and diameters were used as reinforcement in fiber volume fractions of 1.0 and 1.5% to determine the effect of the hybrid reinforcement on the plastic viscosity and shear yield stress.
TL;DR: The combined pressuredecay technique with rheometry is developed to measure the diffusivity of carbon dioxide (CO2) in bitumen at temperatures of 30, 50, and 70 °C and pressures of 2 and 4 MPa.
Abstract: The combined pressure-decay technique with rheometry is developed to measure the diffusivity of carbon dioxide (CO2) in bitumen at temperatures of 30, 50, and 70 °C and pressures of 2 and 4 MPa. Mixing due to shear imposed by a rheometer allows rapid direct measurement of the equilibrium pressure in CO2–bitumen systems accurately. The comparison of the measured equilibrium pressures with the values obtained from the data regression demonstrates significant discrepancies, which can lead to a great deviation in the diffusivity, up to 5-fold different than the true values. The measured values for the diffusivity of CO2 into the bitumen increase with temperature, following the Arrhenius equation. By changing the temperature from 30 °C to 70 °C, the diffusivity increases by 88% at 2 MPa and 54% at 4 MPa. The diffusivity also increases with the pressure, suggesting the ease of diffusion at the presence of the CO2 molecules in the liquid phase. The effect of pressure is more dominant at lower temperatures while ...
TL;DR: In this article, normal and shear stresses in oscillatory shear flow are measured at small and large deformation amplitudes, and new material parameters are then introduced based on Fourier transform rheology and stress decomposition analysis of normal and Shear stress measurements.
Abstract: In this article, normal stresses and shear stresses in oscillatory shear flow are measured at small and large deformation amplitudes. New material parameters are then introduced based on Fourier transform rheology and stress decomposition analysis of normal and shear stress measurements. Furthermore, uniaxial extensional measurements are performed and compared to simulation results using the molecular stress function model. Different behaviors were observed for the polyethylene and polypropylene type blends, which are believed to arise from the different types of long-chain branching (LCB) topology present in each of the systems. The use of the new material parameters proposed and described within this article has the potential to allow for a better understanding of structure-property relationships in industrial LCB materials.
TL;DR: In this article, it was shown that under applied magnetic field both the storage G′ and loss G″ moduli became strain-dependent and the values of G′ decreased with strain, while their ratio (the loss factor), G″/G′, growths with strain.
Abstract: Magnetorheological elastomers (MRE) have been synthesized on the basis of a silicon compound and a mixture of carbonyl iron particles of sizes 3–5 and 40–80 μm. Their viscoelastic properties have been studied by dynamic shear oscillations of various amplitudes on a stress controlled rheometer. The magnetic response of the obtained materials has been examined in a magnetic field applied perpendicular to the shear plane. It has been shown that under applied magnetic field both the storage G′ and loss G″ moduli became strain-dependent. The values of G′ and G″ decrease with strain, while their ratio (the loss factor), G″/G′, growths with strain. The higher magnetic field is the more pronounced the strain dependence is. At small strain (up to 1%) MRE demonstrate a giant (more than 10 times) increase of the moduli. Some features of hysteretic behavior of MRE under simultaneously applied magnetic field and external mechanical force have been elucidated. Temperature has a negligible effect on viscoelastic properties and stability of the developed MRE. A damper on the basis of MRE has been designed and its properties have been examined.
TL;DR: In this paper, the authors used high speed video to evaluate the jetting behavior of weakly elastic dilute linear polystyrene solutions, for molecular weights of 110 −488 kDa.
Abstract: Fluid assessment methods, requiring small volumes and avoiding the need for jetting, are particularly useful in the design of functional fluids for inkjet printing applications. With the increasing use of complex (rather than Newtonian) fluids for manufacturing, single frequency fluid characterisation cannot reliably predict good jetting behaviour, owing to the range of shearing and extensional flow rates involved. However, the scope of inkjet fluid assessments (beyond achievement of a nominal viscosity within the print head design specification) is usually focused on the final application rather than the jetting processes. The experimental demonstration of the clear insufficiency of such approaches shows that fluid jetting can readily discriminate between fluids assessed as having similar LVE characterisation (within a factor of 2) for typical commercial rheometer measurements at shearing rates reaching 104 rad s−1.
Jetting behaviour of weakly elastic dilute linear polystyrene solutions, for molecular weights of 110–488 kDa, recorded using high speed video was compared with recent results from numerical modelling and capillary thinning studies of the same solutions.
The jetting images show behaviour ranging from near-Newtonian to “beads-on-a-string”. The inkjet printing behaviour does not correlate simply with the measured extensional relaxation times or Zimm times, but may be consistent with non-linear extensibility L and the production of fully extended polymer molecules in the thinning jet ligament.
Fluid test methods allowing a more complete characterisation of NLVE parameters are needed to assess inkjet printing feasibility prior to directly jetting complex fluids. At the present time, directly jetting such fluids may prove to be the only alternative.
TL;DR: In this paper, a torsion bar test was proposed to characterize the longitudinal shear mechanism of hot thermoplastic laminates with a uni-directional fiber reinforcement.
Abstract: Intra-ply shear appears during the forming process of hot thermoplastic laminates with a uni-directional fibre reinforcement. This paper proposes a torsion bar test to characterise the longitudinal shear mechanism, which can be performed with a standard rheometer. Sensitivity analyses showed that most reliable shear property measurements can be obtained by using torsion bar specimens with a close to square cross section. The method is implemented in practise and critically evaluated. Storage and loss moduli were determined for carbon UD/PEEK specimens at high temperatures. Non-linear material behaviour was found for relatively small shear strains. The linear regime was focussed on subsequently, where the characteristics were found to be similar to that of a visco-elastic solid or weak gel, confirmed by a dominant storage modulus and a weak frequency dependency. Future work is recommended to be focussed on the large strain regime, for which this paper provides a found basis