Commercial Rheometer Research Articles

High-frequency optimally windowed chirp rheometry for rapidly evolving viscoelastic materials: Application to a crosslinking thermoset

Knowledge of the evolution in the mechanical properties of a curing polymer matrix is of great importance in composite parts or structure fabrication. Conventional rheometry, based on small amplitude oscillatory shear, is limited by long interrogation times. In rapidly evolving materials, time sweeps can provide a meaningful measurement albeit at a single frequency. To overcome this constraint, we utilize a combined frequency- and amplitude-modulated chirped strain waveform in conjunction with a homemade sliding plate piezo-operated rheometer (PZR) and a dual-head commercial rotational rheometer (Anton Paar MCR 702) to probe the linear viscoelasticity of these time-evolving materials. The direct controllability of the PZR, resulting from the absence of any kind of firmware and the microsecond actuator-sensor response renders this device ideal for exploring the advantages of this technique. The high frequency capability allows us to extend the upper limits of the accessible linear viscoelastic spectrum and, most importantly, to shorten the length of the interrogating strain signal (OWCh-PZR) to subsecond scales, while retaining a high time-bandwidth product. This short duration ensures that the mutation number (NMu) is kept sufficiently low, even in fast-curing resins. The method is validated via calibration tests in both instruments, and the corresponding limitations are discussed. As a proof of concept, the technique is applied to a curing vinylester resin. The linear viscoelastic (LVE) spectrum is assessed every 20 s to monitor the rapid evolution in the time and frequency dependence of the complex modulus. Comparison of the chirp implementation, based on parameters such as duration of the experiment, sampling frequency, and frequency range, in a commercial rotational rheometer with the PZR provides further information on the applicability of this technique and its limitations. Finally, FTIR spectroscopy is utilized to gain insights into the evolution of the chemical network, and the gap dependence of the evolving material properties in these heterogeneous systems is also investigated.

A Visual, In-Expensive, and Wireless Capillary Rheometer for Characterizing Wholly-Cellular Bioinks.

Rheological measurements with in situ visualization can elucidate the microstructural origin of complex flow behaviors of an ink. However, existing commercial rheometers suffer from high costs, the need for dedicated facilities for microfabrication, a lack of design flexibility, and cabling that complicates operation in sterile or enclosed environments. To address these limitations, a low-cost ($300) visual, in-expensive and wireless rheometer (VIEWR) using 3D-printed and off-the-shelf components is presented. VIEWR measurements are validated by steady-state and transient flow responses for different complex fluids, and microstructural flow profiles and evolution of yield-planes are revealed via particle image velocimetry. Using the VIEWR, a wholly-cellular bioink system comprised of compacted cell aggregates is characterized, and complex yield-stress and viscoelastic responses are captured via concomitantly visualizing the spatiotemporal evolution of aggregate morphology. A symmetric hyperbolic extensional-flow geometry is further constructed inside a capillary tube using digital light processing. Such geometries allow for measuring the extensional viscosity at varying deformation rates and further visualizing the alignment and stretching of aggregates under external flow. Synchronized but asymmetric evolution of aggregate orientation and strain through the neck is visualized. Using varying geometries, the jamming and viscoelastic deformation of aggregates are shown to contribute to the extensional viscosity of the wholly-cellular bioinks.

Viscoelastic rheology of polymer solution probed by resonant thermal capillary fluctuation

We present a measurement of viscoelastic properties of polymer solutions using resonant thermal capillary fluctuations of the surface of a polymer solution droplet. The instantaneous deflection of a cantilever in contact with the drop surface allows for measuring the nanoscale thermal fluctuations of the interface. From the power spectral density of measured fluctuations, we determine the two components of the rheological (dynamic and elastic viscosity) response of the fluid. Our experimental results were compared with rheological measurements using a classical commercial rheometer. We find a good agreement between the two measurements. Our experiments allow to extend the range for dynamical measurements of rheological properties of the solutions up to 20 000 s−1. Furthermore, our method requires only a small volume of liquid (10 μl) to measure the viscosity and is thus suitable for measurements on precious liquids.

"Gloppiness" Phenomena and a Computer Vision Method to Quantify It.

In this study, we present a rapid, cost-effective Python-driven computer vision approach to quantify the prevalent "gloppiness" phenomenon observed in complex fluids and gels. We discovered that rheology measurements obtained from commercial shear rheometers do show some hints, but do not exhibit a strong correlation with the extent of "gloppiness". To measure the "gloppiness" level of laboratory-produced shower gel samples, we employed the rupture time of jetting flow and found a significant correlation with data gathered from the technical insight panelist team. While fully comprehending the "gloppiness" phenomenon remains a complex challenge, the Python-based computer vision technique utilizing jetting flow offers a promising, efficient, and affordable solution for assessing the degree of "gloppiness" for commercial liquid and gel products in the industry.

Predicting textural attributes and frictional characteristics of topical formulations based on non-linear rheology

A number of analytical procedures (Spectrum Descriptive Analysis (SDA), Quantitative Descriptive Analysis (QDA), and Check All That Apply (CATA)) are used for characterizing sensorial attributes of topical formulations. However, these techniques are evaluated by expert panels/consumers, which are subjective, expensive and time consuming. Despite widespread use of these methods, the techniques do not necessarily aid in the development of innovative formulations and understanding of consumer liking. In addition, the hedonic attributes of a product can significantly dominate the sensation. Therefore, a more rapid, quantitative, and objective approach is required for understanding the formulation factors that governs sensory perception at different points of consumer application. Rheological evaluations of topical formulations were carried out under steady and oscillatory (SAOS and LAOS) rheology using a commercial rheometer. Friction measurements were performed using an in-house built tribometer on non-biological skin model to investigate how surface properties are influenced by application of different topical formulations. Further, a broad range of instrumental texture measurements was performed to characterize the formulations. Principal component analysis was used for dimensionality reduction of the instrumental data. Supervised machine learning was performed on the closely related PCA parameters to develop predictive models. We identified physical parameters relevant to different perceptual attributes by comparing a range of commercial topical formulations with various compositions using rheological and tribological methods. Multi-variate machine learning models were developed where several key instrumental textural attributes and skin feel could be predicted from data obtained from linear and non-linear rheological measurements. Our study shows rheological analysis based on a few material parameters can be effectively used for predicting instrumental sensory attributes that is of relevance to consumer care industry. The machine learning models may benefit development of innovative formulations, valorisation of new materials and serve as a platform for mapping commercial formulations for product optimization. The models can likely shorten design cycle time by screening through large volume of formulations and short list only those with highest potential to be evaluated by a very specialized and expensive human test panel.

Investigation of quasistatic and dynamic mechanical properties of thermoplastic polyurethane magnetorheological elastomers

Thermoplastic magnetorheological elastomers (MRE) are soft magnetic materials with multi stimuli response. As the name suggests, thermoplastic MREs are formed by the suspension of magnetic particles in a thermoplastic elastomer matrix, whose rheological properties can be controlled by temperature. The composite itself can thus be controlled by temperature and magnetic field. In this article, we present the method and results of quasistatic and dynamic mechanical properties of thermoplastic polyurethane MREs (TPU-MREs) based on the observations made on the influence of hardener and plasticizer content from the composition point of view and the directional interdependence of strain and magnetic field on the magnetorheological (MR) effect. Quasistatic tensile and torsion tests followed by dynamic oscillation tests conducted within the linear elastic regime at three different temperatures with and without externally applied magnetic field are performed on the TPU-MRE samples. The tests are conducted with an inhouse developed test setup adapted to a commercial rheometer. The obtained results demonstrate a strong correlation to the change in moduli of the TPU-MRE with respect to change in composition and temperature. From the results obtained, one can conclude that samples with lower hardener content with plasticizer have the highest relative MR effect.

Development of an adaptive coaxial concrete rheometer and rheological characterisation of fresh concrete

Abstract The accessibility to rheological parameters for concrete is becoming more and more relevant. This is mainly related to the constantly emerging challenges, such as not only the development of high-strength concretes is progressing very fast but also the simulation of the flow behaviour is of high importance. The main problem, however, is that the rheological characterisation of fresh concrete is not possible via commercial rheometers. The so-called concrete rheometers provide valuable relative values for comparing different concretes, but they cannot measure absolute values. Therefore, we developed an adaptive coaxial concrete rheometer (ACCR) that allows the measurement of fresh concrete with particles up to d max = 5.5 mm {d}_{{\rm{\max }}}=5.5\hspace{.5em}{\rm{mm}} . The comparison of the ACCR with a commercial rheometer showed very good agreement for selected test materials (Newtonian fluid, shear thinning fluid, suspension, and yield stress fluid), so that self-compacting concrete was subsequently measured. Since these measurements showed a very high reproducibility, the rheological properties of the fresh concrete could be determined with high accuracy. The common flow models (Bingham (B), Herschel–Bulkley, modified Bingham (MB) models) were also tested for their applicability, with the Bingham and the modified Bingham model proving to be the best suitable ones.

Three-dimensional simulation of capillary rheometry for an estimation of extensional viscosity

Abstract It is difficult to directly measure the steady extensional viscosity of thermoplastic composite materials, especially at high extension rates. The famous Cogswell method was derived analytically from the pressure drop of entrance flow in commercial capillary rheometers for estimating the extensional viscosity. However, using Cogswell´s extensional viscosity has always resulted in over-predictions of pressure drop. Recently, the GNF-X (eXtended Generalized Newtonian Fluid) model with a weighted shear/extensional viscosity was proposed to show the typical extension-induced vortex growth in entrance flow simulations. Under given various values of Trouton’s ratio for extensional viscosity, the GNF-X model is introduced to perform three-dimensional flow simulations of capillary rheometry over a range of apparent shear rates. The difference between the predicted pressure drops and the relevant experimental data is minimized such that the estimation of extensional viscosity is optimized herein.

Rod-climbing rheometry revisited.

The rod-climbing or "Weissenberg" effect in which the free surface of a complex fluid climbs a thin rotating rod is a popular and convincing experiment demonstrating the existence of elasticity in polymeric fluids. The interface shape and steady-state climbing height depend on the rotation rate, fluid elasticity (through the presence of normal stresses), surface tension, and inertia. By solving the equations of motion in the low rotation rate limit for a second-order fluid, a mathematical relationship between the interface deflection and the fluid material functions, specifically the first and second normal stress differences, emerges. This relationship has been used in the past to measure the climbing constant, a combination of the first (Ψ1,0) and second (Ψ2,0) normal stress difference coefficients from experimental observations of rod-climbing in the low shear rate limit. However, a quantitative reconciliation of such observations with the capabilities of modern-day torsional rheometers is lacking. To this end, we combine rod-climbing experiments with both small amplitude oscillatory shear (SAOS) flow measurements and steady shear measurements of the first normal stress difference from commercial rheometers to quantify the values of both Ψ1,0 and Ψ2,0 for a series of polymer solutions. Furthermore, by retaining the oft-neglected inertial terms, we show that the "climbing constant"  = 0.5Ψ1,0 + 2Ψ2,0 can be measured even when the fluids, in fact, experience rod descending. A climbing condition derived by considering the competition between elasticity and inertial effects accurately predicts whether a fluid will undergo rod-climbing or rod-descending. Our results suggest a more general description, "rotating rod rheometry" instead of "rod-climbing rheometry", to be more apt and less restrictive. The analysis and observations presented in this study establish rotating rod rheometry combined with SAOS measurements as a prime candidate for measuring normal stress differences in complex fluids at low shear rates that are often below commercial rheometers' sensitivity limits.

Average Rheological Quantities of Cells in Monolayers.

The method of cell monolayer rheology enables quantifying average rheological properties of cell in a single experimental run of few millions cells together in a single layer. Here we describe step-by-step procedure as to how to employ a modified commercial rotational rheometer to run rheological measurement and detect average viscoelastic properties of cells while maintaining the necessary precision level at the same time.

Micronewton shear rheometer performing SAOS using 2 mg of sample

Rheological measurements typically require at least 20–50 mg of sample. We set up a miniaturized sliding-plates shear rheometer (mgRheo) that requires only 2 mg sample or even less. We designed a flexure-based force-sensing device that could measure force ranging from the micronewton to millinewton scale, e.g., 40 μN–400 mN for one particular spring constant. The setup was strain-controlled by a piezostage and could perform standard rheological tests such as small amplitude oscillatory shear, step strain, and stress relaxation. The accuracy and consistencies were evaluated on polydimethylsiloxane viscoelastic standard, entangled poly(hexyl methacrylate), and polystyrene. The obtained phase angles quantitatively agreed with those from commercial rheometers. The exact values of the modulus are prone to the overfilling of the sample. The storage G′ and loss G″ moduli from the mgRheo were systematically higher than those from commercial rheometers (i.e., within 5% with careful trimming or 30% with excessive overfilling). Between 102 and 106 Pa, G′ and G″ were in good agreement with commercial rheometers. Such a setup allowed for general rheometric characterizations, especially obtaining linear viscoelasticity on soft matters that are synthetically difficult to obtain in a large quantity.

Rheometer performs standard testing using a fraction of normal sample size requirements

Flexure-based force-sensing device and a laser interferometer allow device to measure samples less than one-twentieth the mass that most commercial rheometers require.

Characterization of magnetorheological fluids based on capillary magneto-rheometer

Magnetorheological fluids (MRFs) are a class of smart magnetic controlled materials whose rheological properties can be controlled by a magnetic field. These materials have advantages of short response time, high dynamic range and low energy consumption. Due to their excellent properties, MRFs have a widely application potential in the field of impact mitigation. As the shear rate dependent viscosity of MRFs is astonishing for the shear thinning effect, thus it is crucial to study the rheological properties cross a wide range of shear rates for guiding the design and application of MRFs based adaptive impact absorbers. Commercial rotational rheometers are usually used to test the rheological properties of MRFs, but their range of measuring shear rates are limited. Commercial capillary rheometers are designed to measure the rheological behavior over a wide range of shear rates, but they’re usually lack of ability to measure with magnetic field. In order to study the rheological properties of MRFs under higher shear rate and applied magnetic field, a lab-made speed-controlled capillary magneto-rheometer is developed in the presnt work; The expressions for equivalent shear rate and apparent viscosity of MRFs under the dimensional constraint of the set-up are derived. In addition, the theoretical expression of shear rate of MRFs is modified by Rabinowitsch correction. Then, the rheological properties of three particle volume fractions (10%, 15%, and 20%)of MRFs with different magnetic field strengths (6 mT, 13 mT, 20 mT, and 25 mT)are tested and analyzed, and the rheological characteristic curves of MRFs with shear rate range of 101s−1–105s−1 are obtained with the normalized characterization using Mason number. According to the experimental results, the MRFs show an obvious shear thinning phenomenon as shear rate increases, and in the Mason number based normalized characterization, the curves of different particle volume fractions are collapse to a master curve.

A Novel Method of Flow Curve Measurement for Magnetic Fluid Based on Plane Poiseuille Flow

Accurate measurement of the flow curves of magnetic fluid under a uniform field has always been a challenge. In this article, a novel method is proposed to measure the flow curve of magnetic fluids based on plane Poiseuille flow. The measuring system was built and its performance was compared with that of a commercial rheometer. Flow curves of magnetic fluid with different zero-field viscosity were tested under various field strengths. This novel method facilitates direct observation of the flowing behaviors of magnetic fluid under different stresses. By examining the variation trend of viscosity under certain constant stress, a more reliable method to determine the dynamic yield stress of magnetic fluid was used. The dynamic yield stress of the magnetic fluid measured by the new method was larger than the value obtained by the fitting, which is more reliable from an engineering point of view.

Basic principle and good practices of rheology for polymers for teachers and beginners

AbstractWe present a basic principle and good practices of the rheology of polymers, particularly for teachers or lecturers at colleges or universities for educational purposes, as well as for beginner researchers who may refer to this article as their self-learning resources. Basic consideration of the experimental methods using parallel-plate oscillatory rheometer and step-by-step guidelines for the estimation of the power law dependence of storage,G′ and loss,G″ modulus as well as the estimation of the relaxation time atf cross G′−G′′${f}_{\,\mathrm{cross}}^{\,{G}^{\prime }-{G}^{\prime \prime }}$at terminal zone using various approaches such as commercial graphical software, manual graphical approach and commercial rheometer software are highlighted. Good practices for data interpretation using different approaches are described and compared where the outcomes revealed the manual graphical approach or commercial graphical software yield comparable results with the commercial rheometer software. In order to have better insight, several examples and exercises which are applicable for teaching and self-learning activities are also provided.

Frictional contacts between individual woody biomass particles under wet and dry conditions

Friction between wood particles can be a critical property when designing processing equipment for creating cellulosic biofuels and similar natural products. Also, as wood processing is likely to occur year-round, understanding the friction between wet as well as dry wood particles can help design and model equipment, such as screw feeders. Here, a tribo-rheometry method was developed using a commercial rheometer that measured the torque required to rotate two contacting millimeter-scale wood chip particles. First, a range of normal forces were used to find the limits of the experimental method. Torque values were measured for seven pairs of wood chip particles at 1 N normal force under both dry and wet conditions, at both ambient conditions and in a humidity-controlled chamber. The torque required to rotate the wet particles was consistently higher than that of the dry particles, although differences were not quite statistically significant when measurements were performed at ambient conditions. Using humidity control resulted in torque values for wet particles of 1900 μNm and 900 μNm for dry particles. Finally, the friction coefficient was calculated as 0.23 for wet particles and 0.11 for dry particles when humidity was controlled. These frictions coefficients agreed with values for wood reported in the literature. Overall, controlling humidity is strongly recommended to quantify the range of friction for particles that uptake water, including granular systems from biomass to food to powders. Friction higher for wet vs dry wood particles at constant humidity from bar graph on left. On right parallel plate rheomter shown with two wood particles between the plates and axial force pushing plates/particles together and shear force rotating bottom plate. • Tribo-rheometric method developed for controlled moisture friction experiments. • Individual particle friction measured for millimeter-scale wood particles. • Friction coefficients higher for wet versus dry wood particles.

Experimental validation of the extraction of a particle-particle cohesion model (square-force) from simple bulk measurements (defluidization in a rheometer)

The most sophisticated descriptions of particle-particle cohesion rely on extremely sensitive and resource-intensive measurements, often making them impractical for industrial application. The focus here is to experimentally assess the “square-force” cohesion model (Liu et al., 2018), which (i) incorporates the two quantities that dictate interactions, namely cohesive force and energy, and (ii) involves simple bulk measurements to obtain particle-particle cohesion. In particular, square-force model parameters are extracted via a combination of defluidization experiments and corresponding computational fluid dynamics – discrete element method (CFD-DEM) simulations. Defluidization is achieved via an energy-assisted, commercial rheometer such that channeling does not become an obstacle. The resulting square-force cohesion model is then applied to a different system with the same particles, namely pile formation via the free fall of particles. Excellent agreement is found between the measurements and predictions of the angle of repose, indicating that an accurate cohesion model is possible via simple, bulk experiments.

New Progress of Rheology in Industrial Field, Contribution to Development and Enlightenment in Psychorheology

We have tried to measure purely mechanical sensory feelings of cosmetics with using commercial rheometers. To obtain mechanical parameters relating to the score of sensory feeling, we have to measure under the same condition during the evaluation of sensory feeling, that is, the movement of finger and the structure of cosmetics. Sensory feelings of madeup skin can also be measured using stress-controled rotaional rheometers if we fix a measuring part of human body without stress. Understanding the rheological properties of cosmetic emulsions is helpful to design a new product with a desired sensory feeling. Emulsions with high dispersoid concentration have yield point, but high concentration linear polymer solution dose not. This was qualitatively explained with the difference in mobility at the contact point between dispersoids.

Synthesis and rheological characteristics of high viscosity linear polysiloxane carrier fluid-based magnetorheological fluids

This study addresses the synthesis and field-dependent rheological characteristics of novel magnetorheological fluids (MRFs) using high viscosity linear polysiloxanes (HVLPs) as a carrier fluid. First of all, the components and preparation of novel HVLP-based MRFs (HVLP MRFs) were explained in detail and the microscopic images of each component were taken by using scanning electron microscope (SEM). Four HVLP MRF samples with different particle volume fractions of 10, 15, 20, and 26 vol% in the same HVLP carrier fluid viscosity of 800 Pa·s were synthesized to investigate the particle concentration effect on their field-dependent rheological properties. In order to understand the effect of the carrier fluid viscosity, two more HVLP MRF samples with different HVLP viscosities of 140 and 440 Pa·s in the same particle concentration of 26 vol% were also fabricated. In addition, the temperature effect on HVLP MRFs was studied by using the sample with 26 vol% in particle concentration and 140 Pa·s in HVLP viscosity under different operating temperatures of 25 °C, 40 °C, 55 °C and 70 °C. The flow curve measurements of shear stress versus shear rate in the magnetic fields were conducted by using controlled shear rate (CSR) test method with a commercial parallel-plate type rotational rheometer. From the flow curves, the field-dependent rheological properties of HVLP MRFs including static and dynamic yield stresses and the dynamic range (ratio of field on to field off yield stress) were obtained. These material characteristics were then examined as a function of varying particle concentration, varying carrier fluid viscosity, and varying temperature. A conventional commercial MRF (i.e. Lord MRF-126CD) was adopted for comparison study and its rheological properties under different temperatures were also measured and compared with those of HVLP MRFs. Using HVLP carrier fluids, it was demonstrated that the HVLP MRFs exhibited much greater suspension stability than the conventional commercial MRF.

First step in modeling the flow table test to characterize the rheology of normally vibrated concrete

A precise measurement of the rheological properties of concrete is the first step to quantitatively evaluate the placing and casting process. Both yield stress and plastic viscosity of flowable concrete can be conveniently estimated through a model correlating them with the slump flow test results. However, there has been no report on estimating the plastic viscosity of normally vibrated concrete and that of mortar constituting the concrete. This paper provides a model using the flow table test, specified in ASTM C 1437, to estimate the Bingham parameters of mortar. The model is based on the volume-of-fluid simulations of a non-Newtonian non-thixotropic homogeneous fluid. The estimated Bingham parameters are compared with the measurements obtained using two commercial rheometers. The bias of rheological measurement and effect of mortar film thickness on rheology are also discussed. Finally, the Bingham parameters of wet-sieved mortar allows us to characterize the range of Bingham parameter of mortar constituting normally vibrated concrete.