Traditional Rheometer Research Articles

Virtualized Viscosity Sensor for Onboard Energy Management

Essential for decision-making, measurement is a cornerstone of various fields including energy management. While direct methods exist for some quantities like length, most physico-chemical properties require indirect assessment based on observable effects. Historically, pressure was measured by the water column height, and temperature by mercury expansion. Recent advancements in artificial intelligence (AI) offer a transformative approach by combining vast datasets with traditional measurements. This holds immense potential for applications facing extreme conditions and involving complex fluids where measurement is extremely challenging (over 1500 K and 5 MPa). In this study, an AI model is evaluated to replace online rheometers (293–1173 K, 0.15–3.5 MPa). A machine learning model utilizes a neural network with up to 8000 neurons, eight hidden layers, and over 448 million parameters. Trained, tested, and validated on three experimental databases with over 600 test conditions, the New Generation Predicted Viscosity Sensor (NGPV sensor) achieves exceptional accuracy (less than 4.8 × 10−7 Pa·s). This virtualized sensor proves highly relevant for hypersonic airbreathing applications involving fuel degradation and energy conversion. It maintains excellent predictability (accuracy below 6 × 10−6 Pa·s) even at flow rates 10 times higher than calibration, surpassing traditional rheometers limited by calibration needs and a lower viscosity measurement threshold (10−4 Pa·s).

Bubbles as high-frequency rheometers for soft matter characterization

Precise knowledge of bubble dynamics in tissue is essential for optimizing both ultrasound imaging and ultrasound therapy. Great efforts have therefore been made, over the past decade, to model the behavior of (micro)bubbles in viscoelastic materials. This has led to a series of models based on modified Rayleigh–Plesset equations. Last to date, we propose a novel generalized model build on finite strain theory and relaxation functions. At this stage however, the bottle neck remains our limited knowledge of tissue viscoelasticity at high strain rates, which is a necessary input to any theoretical model. Indeed, traditional rheometers cannot reach frequencies above 1kHz, which is 3 orders of magnitude below the desired MHz frequencies. We will show how ultrasound-driven bubbles can be used as microscale rheometers. More specifically, we use the volumetric oscillations of (monodisperse) phospholipid-coated microbubbles embedded in hydrogels to measure the storage and loss moduli in the MHz frequency range. In addition, we can bridge the gap between kHz and MHz using the surface modes of cylindrical microbubbles trapped in micropits. These oscillations can be both modelled and simulated, and provide access to the effective surface tension and viscosity in the range of 50 to 500 kHz.

Bovine Serum Albumin Hydrogel Formation: pH Dependence and Rheological Analyses.

In vitro evaluation of the physical properties of biopolymer-based hydrogels can help in understanding certain phenomena, such as liquid-liquid phase separation. The formation of bovine serum albumin (BSA) hydrogels was investigated in the pH range of 1.0 to 4.0. Hydrogels were formed in the pH range of 3.0 to 4.0, whereas viscous solutions were formed in the pH range of 1.5 to 2.5. Unexpectedly, formation of BSA hydrogel was observed in extremely acidic condition (pH 1.0). The circular dichroism spectra of BSA solutions were recorded at pH values of 1.0, 2.0, 3.0, and 7.0, and α-helix contents were determined from the ellipticity data at 222 nm. The α-helix content decreased with a decrease in pH, and this decrease was associated with the partial denaturation (F-isoform) and the denaturation (E-isoform) of BSA. However, the α-helix contents at pH 1.0 and 3.0 were similar. BSA hydrogels at pH 1.0 and 3.5 showed similar dynamic viscoelastic properties, further supporting the stereo structural change of BSA from the denatured E-isoform to the partially denatured F-isoform at pH 1.0. The study also focused on measuring viscoelasticity, a fundamental physical property of hydrogels, using traditional rheometer and with minimal sample volume. A highly reproducible procedure for measuring the viscoelastic properties of hydrogels was established using sample volumes of 200 and 350 μL.

Experimental study on low-cycle fatigue and recovery properties of viscous material for viscous damping wall

This paper aims to study the low-cycle fatigue property and recovery properties of viscous material. The authors designed a Self-Stabilization Dynamic Sandwich-Type Shear (S-DSTS) test device, which allows the static recovery of semisolid materials that can not be achieved in the traditional rheometer. A series of recovery tests with different static recovery times and low-cycle fatigue tests with different strain amplitudes and loading frequencies were conducted on the polyisobutylene-B12 (PIB–B12) by this device. The test data on low-cycle fatigue and recovery properties of PIB-B12 were evaluated by the storage modulus, loss modulus, loss factor, velocity exponent, parameter decay ratio, and recovery coefficient. The results show that each parameter's degradation rate and degradation degree increase significantly with the rise of strain amplitude. The low-cycle fatigue property of PIB-B12 is less affected by the loading frequency, and the degradation rate and degradation degree of all parameters are similar under different loading frequencies. The PIB-B12 has excellent recoverability and static recovery showing that the mechanical parameters of PIB-B12 could restore to more than 65% and 92% of the original magnitude after short-term and long-term intervals, which ensures a reliable energy absorption property during aftershocks. The velocity exponent of PIB-B12 shows minor variations under different strain amplitudes and loading frequencies.

Microrheometer for Biofluidic Analysis: Electronic Detection of the Fluid-Front Advancement.

The motivation for this study was to develop a microdevice for the precise rheological characterization of biofluids, especially blood. The method presented was based on the principles of rheometry and fluid mechanics at the microscale. Traditional rheometers require a considerable amount of space, are expensive, and require a large volume of sample. A mathematical model was developed that, combined with a proper experimental model, allowed us to characterize the viscosity of Newtonian and non-Newtonian fluids at different shear rates. The technology presented here is the basis of a point-of-care device capable of describing the nonlinear rheology of biofluids by the fluid/air interface front velocity characterization through a microchannel. The proposed microrheometer uses a small amount of sample to deliver fast and accurate results, without needing a large laboratory space. Blood samples from healthy donors at distinct hematocrit percentages were the non-Newtonian fluid selected for the study. Water and plasma were employed as testing Newtonian fluids for validation of the system. The viscosity results obtained for the Newtonian and non-Newtonian fluids were consistent with pertinent studies cited in this paper. In addition, the results achieved using the proposed method allowed distinguishing between blood samples with different characteristics.

Identification and Characterization of Asphalt Concrete Phases Using Nanoindentation Creep Analysis

AbstractAsphalt researchers have studied only the bulk state (liquid or semisolid) of asphalt binder using traditional rheometers. In roadway pavements, an asphalt binder never exists in a liquid o...

The rising motion of spheres in structured fluids with yield stress

The rising of spherical bodies in structured fluids with yield stress is studied. The system is a suspension of hydrogenated castor oil colloidal fibers in a surfactant micellar solution. The fiber network confers to the fluid a viscoelastic behavior, with a well-defined yield stress, which increases with increasing fiber concentration. Various fluids with different fiber contents are prepared and rheologically characterized. A home-made time-lapse photography setup is used to monitor the time evolution position of the spherical particles, and the rising motion of both hollow spheres and air bubbles, in the diameter range 65–550 μm, is measured. The experiments last as long as several weeks, corresponding to significantly low measured velocities. Finite element simulations are performed to support the experimental data, assuming both interfacial slip and no slip conditions. The fluid dynamic phenomenon is studied and discussed in terms of dimensionless numbers, such as yield ratio, Bingham number, and Stokes drag coefficient. The results are novel for the system (suspending medium and hollow spheres) and for the covered Bingham number range, which is extended over three orders of magnitude in comparison with already available literature results. Our values provide quantitative data of the mechanical properties (i.e., yield stress value) at very low shear rates, in a prohibitive range for a traditional rheometer, and agree with the macroscopic rheological response. Moreover, the important role of the power law index n of the Herschel-Bulkley model, used to fit the data, has been highlighted. Our results, based on a Bingham-like fluid, are compared with the experimental data already available with Carbopol, treated as a Herschel Bulkley fluid with n = 0.5. The results could have important implications in the fabric and personal care detergency, a technological area where many fluids have composition and show rheological properties similar to those considered in the current work.

Rheology of complex fluids with vibrating fiber-optic sensors

We demonstrate a new optical rheometer where a fiber Bragg grating sensor (FBG) detects the periodical strain caused by the oscillations of a string tightened within a sample fluid. We show that the viscoelastic moduli of complex fluids can be obtained instantaneously from the FBG optical backreflection signal, without need of any current flow in the wire or magnetic field that could affect the sample chemistry. After a validation with known-viscosity solutions, the technique is employed to monitor the phase transition of a sol-gel compound. The results provide an insight in the early-stage gelation dynamics that cannot be obtained with traditional rheometers, and allow to clearly identify the gel point as the intersection of the viscoelastic moduli.

In situ viscoelastic properties of insoluble and porous polysaccharide biopolymer dextran produced by Leuconostoc mesenteroides using particle-tracking microrheology

With growing interests in using bacterial biopolymers in geotechnical practices, identifying mechanical properties of soft gel-like biopolymers is important in predicting their efficacy in soil modification and treatment. As one of the promising candidates, dextran was found to be produced by Leuconostoc mesenteroides. The model bacteria utilize sucrose as working material and synthesize both soluble and insoluble dextran which forms a complex and inhomogeneous polymer network. However, the traditional rheometer has a limitation to capture in situ properties of inherently porous and inhomogeneous biopolymers. Therefore, we used the particle tracking microrheology to characterize the material properties of the dextran polymer. TEM images revealed a range of pore size mostly less than <TEX>$20{\mu}m$</TEX>, showing large pores > <TEX>$2{\mu}m$</TEX> and small pores within the solid matrix whose sizes are less than <TEX>$1{\mu}m$</TEX>. Microrheology data showed two distinct regimes in the bacterial dextran, purely viscous pore region of soluble dextran and viscoelastic region of the solid part of insoluble dextran matrix. Diffusive beads represented the soluble dextran dissolved in an aqueous phase, of which viscosity was three times higher than the growth medium viscosity. The local properties of the insoluble dextran were extracted from the results of the minimally moving beads embedded in the dextran matrix or trapped in small pores. At high frequency (<TEX>${\omega}>0.2Hz$</TEX>), the insoluble dextran showed the elastic behavior with the storage modulus of ~0.1 Pa. As frequency decreased, the insoluble dextran matrix exhibited the viscoelastic behavior with the decreasing storage modulus in the range of <TEX>${\sim}0.1-10^{-3}Pa$</TEX> and the increasing loss modulus in the range of <TEX>${\sim}10^{-4}-1\;Pa$</TEX>. The obtained results provide a compilation of frequency-dependent rheological or viscoelastic properties of soft gel-like porous biopolymers at the particular conditions where soil bacteria produce bacterial biopolymers in subsurface.

The Effect of Consistency and Freeness on the Yield Stress of Chemical Pulp Fibre Suspensions

To study the influence of mechanical treatments on the yield stress of chemical pulp suspensions, a traditional rheometer, coupled with local velocity measurements (ultrasonic Doppler velocimetry), was used to measure the yield stress of two types of commercial chemical pulp suspensions with different freeness values at mass concentrations (consistencies) ranging from 0.5 to 1.5%. Over the range of consistencies tested, the yield stress was found to depend on the consistency through a power law relationship for all tested samples. Moreover, the results showed that as the freeness decreased, the yield stress of hardwood suspensions increased to a maximum value then decreased. This variation in yield stress was also observed in softwood suspensions with mass concentrations above 1%. However, when the consistency was lower than 0.75%, the yield stress of softwood suspensions increased with decreasing freeness.This behaviour can be understood based on the underlying fibre properties of fibrillation, curl, and stiffness, suggesting that fibre morphology plays a significant role on the yield stress of pulp suspensions over the concentration range studied.

Dynamics of bead formation, filament thinning and breakup in weakly viscoelastic jets

The spatiotemporal evolution of a viscoelastic jet depends on the relative magnitude of capillary, viscous, inertial and elastic stresses. The interplay of capillary and elastic stresses leads to the formation of very thin and stable filaments between drops, or to ‘beads-on-a-string’ structure. In this paper, we show that by understanding the physical processes that control different stages of the jet evolution it is possible to extract transient extensional viscosity information even for very low viscosity and weakly elastic liquids, which is a particular challenge in using traditional rheometers. The parameter space at which a forced jet can be used as an extensional rheometer is numerically investigated by using a one-dimensional nonlinear free-surface theory for Oldroyd-B and Giesekus fluids. The results show that even when the ratio of viscous to inertio-capillary time scales (or Ohnesorge number) is as low as Oh ~ 0.02, the temporal evolution of the jet can be used to obtain elongational properties of the liquid.

Using Screening Test Results to Predict the Effective Viscosity of Swollen Superabsorbent Polymer Particles Extrusion through an Open Fracture

Superabsorbent polymer particles, also called preformed particle gels (PPGs), have been successfully applied to reduce water production and enhance oil production in mature reservoirs with fractures or super-high-permeability streaks/channels. The applied particles usually range in size from a few hundred micrometers to a few millimeters and are irregular in shape, which make it impossible to measure their rheology behavior using a traditional rheometer. A simple method, a screen model test, was designed to evaluate the rheological behavior of the swollen PPG. The results show that a swollen PPG is a shear-thinning material with properties that can be expressed using a power-law equation from which an apparent consistency constant and an apparent flow index can be obtained. Considering the shear-thinning properties, we first developed a theoretical mathematical model using a general power-law equation to predict the pressure gradient of a swollen PPG during its extrusion through a fracture. Then, we modified the model by correlating screen test results with fracture experiment results so that the apparent consistency constant and the apparent flow index obtained from the screen tests were introduced to replace the consistency constant and flow index from the general power-law equation. These equations correlated effective viscosity with flow rate, fracture width, apparent consistency constant, and apparent flow index together. The newly developed correlations were validated, and the results showed that a single group of screen test measurements can be applied to determine the effective viscosity of a PPG in a fracture with limited errors.

Microrheology of complex fluids using optical tweezers: a comparison with macrorheological measurements

The increasing interest in the mechanical properties of complex systems at mesoscopic scale has recently fueled the development of new experimental techniques, collectively indicated as microrheology. Unlike bulk-based approaches (macrorheology), these new techniques make use of micrometric probes (usually microspheres) which explore the mechanical properties of the surrounding medium. In this paper we discuss the basic idea of microrheology and we will focus on one specific technique based on optical tweezers (OT). The discussion starts from Newtonian fluids to tackle the more general case of complex fluids, also showing results of these techniques on solutions of a relevant biomolecule: hyaluronic acid (HA). In particular, we study the viscoelastic properties of low molecular weight HA (155?kDa) at low ionic strength over an extended frequency range (0.1?1000?Hz) and in a wide range of concentrations (0.01?20?mg?ml?1), which include both the dilute and semidilute regime. In the concentration range here explored and within the test frequencies covered by our techniques, samples prevalently exhibit a viscous behavior, the elastic contribution becoming significant at the highest concentrations. By comparing OT outcomes to those obtained by a traditional rheometer, we found that they were in good agreement in the overlapping frequency range of the two techniques, thus confirming the reliability of the microrheological approach.

Plastic-to-Elastic Transition in Aggregated Emulsion Networks, Studied with Atomic Force Microscopy−Confocal Scanning Laser Microscopy Microrheology

In this paper, we demonstrate how the simultaneous application of atomic force microscopy (AFM) and confocal scanning laser microscopy (CSLM) can be used to characterize the (local) rheological properties of soft condensed matter at micrometer length scales. Measurement of AFM force curves as a function of the indentation amplitude and speed (magnitude and direction) can produce a "mechanical fingerprint" that contains information about material stiffness, hysteretic losses, and time scales for stress relaxation and/or network recovery. The simultaneous CSLM visualization of changes in the material's structure provides complementary information about how the material accommodates the indentation load. Since these experiments are done on areas of O(100 microm2) on materials having a surface of O(1 cm2), the measurements can be repeated on "fresh" material many times, contrary to traditional rheometers where the whole sample is loaded at once. As a particular example, we consider the case of a network of aggregated water-in-oil (W/O) emulsion droplets, in which the mechanical behavior changes drastically over time. Whereas the freshly prepared material shows a soft plastic behavior, after a time lapse of several weeks, the very same sample shows a much stiffer and elastic response. This drastic change in behavior is clearly reflected both in the signature of the AFM force curves and in (the reversibility of) the structural deformations observed with CSLM. The fact that these drastic mechanical changes take place without significant changes in the structure of the material (before loading) indicates that the stiffening of the droplet network is caused by an increase in the strength of the bonds between droplets. A remarkable finding for the elastic droplet network is that, while the structure recovers completely after the indenter is taken out, there is still an appreciable hysteresis in the force curves, indicating that dissipation also occurs. This hysteresis was not found to depend on the indentation speed.

Using Self-Sensing Techniques to Produce a Small, Robust, Inexpensive Rheometer

Abstract Self-sensing is the technique of using a transducer to both actuate and sense concurrently, therefore eliminating the need for separate sensors. A sensorless rheometer could be much smaller, simpler and more robust than traditional designs. One application where such a rheometer would be desired is the in-situ measurement of curing bone cement in orthopaedic surgery. A set of equations was developed that models the relationship between force, motion and back-e.m.f. generation for a class of electromagnetic actuators. This enables velocity, displacement and force to be self-sensed from voltage measurements only. This self-sensing was validated on a conventional linear electromagnetic actuator, and a small rotary moving magnet device, which was designed to be a small self-sensing rheometer. The accuracy of the estimation was assessed and shown to compare favourably with measured data. The actuators were then used to construct simple rheometers to measure bone cement. Rheological models were used to calculate storage and loss moduli and dynamic viscosity from the self-sensed values of displacement, velocity and torque. The accuracy of these self-sensing rheometers was verified against a traditional rheometer using a silicone fluid and a polyethylene oxide solution. The self-sensing rheometers were used to characterise acrylic bone cements during curing, reinforcing and extending upon previous results. The elimination of sensors meant that it was possible to produce a small, inexpensive rheometer with a very simple structure. This indicates there is potential to develop small rheo-transducers for certain applications.

Measurement of rheological properties of ultrathin lubricant films at very high shear rates and near-ambient pressure

In liquid-lubricated bearings used in experimental near-contact magnetic recording devices, rheological properties of lubricant films at very high shear rates (up to about 109 s−1) and at near-ambient pressure are required. In this extremely high shear rate regime, shear thinning (non-Newtonian behavior) becomes extremely important. A rheometer is designed and constructed that makes it possible to study the rheology of lubricants at extremely high shear rates. Since traditional rheometers are limited to moderate shear rates due to viscous heating, the design used in this study is based on a magnetic disk drive configuration in which an ultrathin film of lubricant is sheared between a magnetic disk and a slider at relatively low sliding speeds. By monitoring the film thickness between the slider and the disk using a capacitive method, it is possible to accurately measure the shear rate. Two different types of perfluoropolyether lubricants have been studied up to shear rates of 107 s−1, and these data have been compared to previously published data.